CA2033545A1 - Method for the removal of monovalent ions from metal sulfate solutions - Google Patents
Method for the removal of monovalent ions from metal sulfate solutionsInfo
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Abstract
METHOD FOR REMOVAL OF MONOVALENT IONS FROM
METAL SULFATE SOLUTIONS BY ELECTRODIALYSIS
ABSTRACT
Monovalent ions of chlorine, bromine, fluorine, sodium, potassium and thallium, are efficiently removed from metal sulfate-containing solutions by electrodialysis using alternating monovalent anion permselective membranes and cation exchange membranes or monovalent cation permselective membranes. Both monovalent anions and cations are removed, or only monovalent anions are selectively removed from the metal sulfate solutions. Monovalent anions may be substantially completely removed in a staged process. The method is also useful for the removal of monovalent anions from sodium and potassium sulfate solutions. The sulfate solutions may contain at least one metal other than zinc preferably chosen from Cu, Co, Ni, Mn, Fe, Mg, Cd, Na and K, and which may be present in a dominant amount.
Electrodialysis is carried out in one or more stages under turbulent flow conditions, at up to 60°C, a differential membrane pressure of less than 150 kPa, a current density of about 10 to 500 A/m2, preferably 50 to 300 A/m2, and a pH in ranges between values from about 1 to about 9, depending on the metal in the feed. Deposition of metals on the electrodes is minimized. Multi-stage electrodialysis enables the attainment of very low monovalent ion concentrations and the minimizing of metal losses.
METAL SULFATE SOLUTIONS BY ELECTRODIALYSIS
ABSTRACT
Monovalent ions of chlorine, bromine, fluorine, sodium, potassium and thallium, are efficiently removed from metal sulfate-containing solutions by electrodialysis using alternating monovalent anion permselective membranes and cation exchange membranes or monovalent cation permselective membranes. Both monovalent anions and cations are removed, or only monovalent anions are selectively removed from the metal sulfate solutions. Monovalent anions may be substantially completely removed in a staged process. The method is also useful for the removal of monovalent anions from sodium and potassium sulfate solutions. The sulfate solutions may contain at least one metal other than zinc preferably chosen from Cu, Co, Ni, Mn, Fe, Mg, Cd, Na and K, and which may be present in a dominant amount.
Electrodialysis is carried out in one or more stages under turbulent flow conditions, at up to 60°C, a differential membrane pressure of less than 150 kPa, a current density of about 10 to 500 A/m2, preferably 50 to 300 A/m2, and a pH in ranges between values from about 1 to about 9, depending on the metal in the feed. Deposition of metals on the electrodes is minimized. Multi-stage electrodialysis enables the attainment of very low monovalent ion concentrations and the minimizing of metal losses.
Description
METHOD FOR REMOVAL OF MO~OVALENT IONS FROM
METAL SULFATE SOLUTIONS BY ELECTRODIALYSIS
This invention relates to the removal of monovalent ions from metal sulfate solutions by electrodialysis.
BACKGROUND OF THE INVENTION
Most hydrometallurgical processes for the recovery of metals in a sulfate system involve the formation and treatment of metal sulfate solutions and may include e]ectrowinning, solvent extraction or electrorefining. These processes may encounter problems with the presence of monovalent ions, especially halides such as chloride, fluoride and bromide, or cations such as sodium, potassium and thallium. Such monovalent ions may be naturally present in the ore or concentrate or may be added during the processing of the ore or concentrate. For example, small amounts of chloride, usually in the form of sodium chloride, may be added to obtain a good quality copper or to control the presence of silver.
In many cases it will be important to control the amount of monovalent ions, especially halides, in recirculating solutions, particularly in processes for producing high-purity metals. In many of these processes, a removal step may be required or is actually a step in the process. For example, according to US 4 338 168, copper concentrates are leached with a chloride and bromide-containing solutionl and solution is subsequently purified by adding copper to remove the halides. This process has the disadvantage of requiring the addition of copper for halide removal. According to US 4 698 139, base metals that include Cu, Co, Ni, Mn, Mg, Zn and Fe are electrolytically recovered from materials containing chloride and fluoride. The materials are leached, metal sulfates are crystallized, the crystals are washed with return acid, then leached in water, and metal is recovered by electrolysis. The halides are removed from the crystallization mother liquor by evaporation. The disadvantages of this process include the inclusion of halides in the crystallized sulfates and the formation of halides by evaporation. According to US 4 874 436, a high-purity copper is electrolytically deposited in a diaphragm cell from a nitric acid electrolyte also containing silver. Chloride is added to precipitate silver, and after the removal of silver, the solution is recirculated to the cell. This process will require the careful control of chloride addition and concentration to prevent the deleterious effects of chloride in the cell. It must also be noted that it is important to control the halide content of electrolytes used in electrolytic processes to avoid anode scaling, erosion and undesirable halogen generation. Other disadvantages of the various halide removal processes or steps include the often incomplete removal of the halides requiring additional removal steps, and high costs.
In other processes it may also be necessary to control the content of halides or to remove halides to avoid their harmful effects on processes and equipment. Such processes may include the treatment or recovery of sodium or potassium sulfate, especially when the pure salts are desired.
The removal of ions from solutions could be carried out by methods that may include electrodialysis, which is well documented. The removal of monovalent ions from zinc sulfate electrolyte by electrodialysis has been patented by the same assignee as of the present invention (US Patent 4 715 939).
Neither this reference nor the other references, however, disclose the use of electrodialysis in purification of metal sulfate-containing solutions for the recovery of metal other than zinc, or the removal by electrodialysis of monovalent ions such as ions of chlorine, bromine, fluorine, sodium, potassium and thallium from metal sulfate solutions containing metals other than zinc.
SUMMARY OF THE INVENTION
We have now found that the halides as well as monovalent cations can be efficiently removed from metal sulfate solutions containing dominant metal other than zinc by electrodialysis.
According to the invention, metal sulfate-containing solution containing at least one metal other than zinc, and containing monovalent ions, is treated by passing solutions through an electrodialysis unit to remove both monovalent anions and monovalent cations or monovalent anions alone. The method of the invention may also be successfully used for the removal of monovalent anions from solutions that contain monovalent cations such as sodium and potassium. Preferably, the metal other than zinc is chosen from the group consisting of Cu, Co, Ni, Mn, Fe, Mg, Cd Na and K. A metal of this group may be present in a dominant amount with other metals of this group being present in lesser amounts. The electrodialysis unit includes a number of alternating concentrate and diluate compartments separated by alternating cationic and anionic membranes, and an anode and a cathode compartment containing an anode and a cathode, respectively. The anionic and cationic membranes are selected from suitable monovalent ion permselective membranes for the removal of both monovalent anions and cations. When selective removal of monovalent anions is desired and removal of monovalent cations is not required, monovalent anion permselective membranes are used, and the cationic membranes are selected from the generally available cationic membranes. Metal sulfate-containing solution is passed through the diluate cells and the current applied to the electrodes causes monovalent ions to pass from the diluate compartments through the membranes into the concentrate in the concentrate compartments. Any metal deposition on the electrodes is controlled by one or more of a number of means that include the controlling of the compositions and flow rate of an electrode rinse solution that is circulated through the anode and the cathode compartmentsi the arranging of the alternating membranes such that the anode compartment and cathode compartment are separated from the adjacent diluate or concentrate compartments by a monovalent 5 ,~033~4~
anion permselective membrane; and the use of a cathode material that favours hydrogen evolution over metal deposition. Because halide, especially fluoride, removal is pH dependent, the pH of the electrolyte is carefully controlled within predetermined ranges. The range is dependent on the solution being treated, usually on what metal is dominant. Generally, values of the pH are in the range of about one to nine. A less strict control of pH is required when the anion removal is restricted to anions of chlorine or bromine or both. The electrodialysis may be carried out in one or more stages depending on the concentration of monovalent ions in the metal sulfate solutions to be treated and/or the desired level of these ions and the metal ions in the treated solutions. ~y choosing appropriate conditions, the method of the invention can result in the effective removal in one or more stages of 90~ or better of the monovalent ions, especially the ions of chlorine, bromine, fluorine, sodium, potassium and thallium from the rnetal sulfate solutions. In many cases, anions of chlorine, fluorine and bromine may be substantially completely removed.
The content of the monovalent ions in treated solutions may be readily controlled in the process or in the treated solution.
According to the invention, there is provided a method for the treatment by electrodialysis of metal sulfate-containing solution containing at least one metal other than zinc and containing concentrations of monovalent ions including at least one ion chosen from the group consisting of cations of thallium, sodium and potassium, and of anions of chlorine, bromine and fluorine, said method comprising the steps of feeding metal sulfate-containing solution to diluate compartments of an electrodialysis unit comprising a multiplicity of alternating monovalent cation permselective exchange membranes and monovalent anion permselective exchange membranes, said membranes defining alternating diluate and concentrate compartments, an anode compartment and a cathode compartment, an anode positioned in the anode compartment and a cathode positioned in the cathode compartment; applying an electrical current between the anode and the cathode at a value such that the value of the corresponding current density is in the range of about 10 A/m2 to 500 A/m2; feeding metal sulfate-containing solution at a controlled pH having a value in ranges between values from about 1 to about 9 to said diluate compartments; circulating flows of diluate and concentrate through the diluate and concentrate compartments, respectively, at a linear velocity sufficient to maintain turbulent flow in said compartments; withdrawing at least a portion of the circulating diluate as the treated metal sulfate-containing solution with reduced concentrations of said monov~lent ions; and withdrawing at least a portion of the circulating concentrate.
According to a second embodiment, there is provided a method for the treatment by electrodialysis of metal sulfate-containing solution containing at least one metal other than 7 2~3354~
zinc and containing concentrations of monovalent anions including at least one anion chosen from the group consisting of anions of chlorine, bromine and fluorine, said method comprising the steps of feeding metal sulfate-containing solution to diluate compartments of an electrodialysis unit comprising a multiplicity of alternating cation exchange membranes and monovalent anion permselective exchange membranes, said membranes defining alternating diluate and concentrate compartments, an anode compartment and a cathode compartment, an anode positioned in the anode compartment and a cathode positioned in the cathode compartment; applying an electrical current between the anode and the cathode at a value such that the value of the corresponding current density is in the range of about 10 A/m2 to 500 A/m2; feeding metal sulfate-containing solution at a controlled pH having value in ranges between values from about 1 to about 9 to said dilute compartments; circulating flows of diluate and concentrate through the diluate and concentrate compartments, respectively, at a linear velocity sufficient to maintain turbulent ~low in said compartments; withdrawing at least a portion of the circulating diluate as the treated metal sulfate-containing solution with reduced concentrations of monovalent anions; and withdrawing at least a portiGn of the circulating concentrate.
Preferably, the at least one metal other than zinc is chosen from the group consisting of copper, cobalt, nickel, manganese, iron, magnesium, cadmium, sodium and potassium.
8 Z~33~45 Preferably, one Gf the metals of this group is present in a dominant amount in the metal sulfate-containing solution.
It is an aspect of the present invention to provide a method for the removal of monovalent ions from metal sulfate-containing solutions containing metal other than zinc.
It is another aspect to provide a method for the removal of both monovalent cations and monovalent anions from metal sulfate-containing solutions containing metal other than zinc by electrodialysis.
It is a further aspect to provide a method for the selective removal of monovalent anions from metal sulfate-containing solutions containing metal other than æinc by electrodialysis.
It is yet another aspect to provide a method for treating metal sulfate-containing solution by electrodialysis for the removal of monovalent ions and controlling the concentration of the monovalent ions in treated solution.
These and other aspects of the present invention will become apparent from the following detailed description of the method of the present invention.
DETAILED DES~RIPTION
Metal sulfate solutions that may be treated according to the method of the present invention include solutions obtained from or present in the treating of metal-containing materials such as ores, concentrates and metallurgical process intermediate products with sulfuric acidl or solutions used 9 ~ 354S
for extracting metal by electrolytic or solvent extraction processes. Metal sulfate solutions treated also include solutions encountered in the processing of magnesium, sodium and potassium salts. The metal sulfate solutions contain at least one metal other than zinc. The at least one metal other than zinc may be present in a dominant amount and is, preferably, chosen from the group consisting of Cu, Co, Ni, Mn, Fe, Mg, Cd, Na and K. The metal sulfate solutions may also contain other metals that may accompany the preferred metal in the sulfate solutions such as, for example, arsenic, antimony, zinc, lead, bismuth, silver, tin and calcium, as well as the metals of above-recited group present in amounts smaller than the amount of the metal that i5 dominant in the solutions. The metal sulfate solutions include monovalent ions comprising at least one monovalent cation or at least one monovalent anion. Thus, for example, the metal sulfate solution containing monovalent ions may be a copper sulfate-containing solution wherein copper is the dominant metal, and other metals such as zinc, arsenic, iron, silver, nickel and other metals may be present in ionic form. The metal sulfate solutions are subjected to a treatment to remove monovalent anions such as the anions of chlorine, bromine, fluorine, and monovalent cations such as the cations of sodium, potassium and thallium. Any nitrate, if present in solution, will be removed with the other monovalent ions. As will be explained hereinafter, only monovalent anions may be selectively removed or both monovalent anions and cations may be removed. As will be explained, the method may also be used to remove monovalent 10 ;~033~4~
anions from ~etal solutions wherein the metal is a monovalent ion such as sodium or potassium.
Metal sulfate-containing solution, present in a process wherein such solution occurs or is treated, is fed to an electrodialysis unit. The electrodialysis unit comprises a multiplicity of vertically arranged, alternating monovalent anion permselective exchange membranes and cation exchange membranes or monovalent cation permselective exchange membranes, a cathode compartment and an anode compartment.
The choice of membranes is important. When only monovalent anions are to be removed, the use of a combination of monovalent anion permselective membranes and general cation exchange membranes (limited permselectivity for mono over multivalent cations) makes it possible to remove monovalent anions selectively from the solution. This combination of membranes can be advantageously used when monovalent cations are present in small amounts. When both monovalent anions and monovalent cations are to be removed, a combination of monovalent anion and monovalent cation permselective membranes is used. Such combination will, therefore, make it possible to separate monovalent ions from multivalent ions, and to concentrate the monovalent cations and the monovalent anions.
The metal sulfate-containing solution thereby becomes depleted in these ions.
We have found that suitable monovalent cation permselective membranes are, for example, strongly acidic membranes which 11 ~(3;~35~5 have a membrane matrix of a styrene di-vinyl benzene co-polymer on a polyvinyl chloride base and possess sulfonic acid radicals (R-SO3H3 as active groups. The active groups comprise 3-4 milli-equivalents per gram of dry resin which is satisfactory to provide the desired selectivity for monovalent ions. Suitable monovalent cation permselective membranes are specially treated SelemionTM CMV, SelemionTM Experimental A
(specially treated on one face), and Selemion1-M Experimental B or SelemionTM CSR (both surfaces specially treated) and specially treated SelemionTM CMR. If the object is to remove only monovalent anions such as anions of chlorine, bromine and fluorine, and not monovalent cations, the choice of the cation membrane can be extended to include others available on the market such as, for example, those with sulfonic acid radicals (R -SO3 H) as the active groups at 3-5 milli-equivalents per gram of dry resin, e.g., SelemionTM CMV.
Suitable monovalent anion permselective membranes are, for example, strongly basic membranes with quaternary ammonium active groups, such as, for example, derived from trimethylamine (for example, R-N(CH2)3.Cl)l at 3-4 milli-equivalents per gram of dry resin, and having a matrix of a styrene di-vinyl benzene co-polymer on a polyvinyl chloride base. SelemionTM ASV, ASS or ASR, which is permselective for monovalent anions, particularly anions of chlorine, bromine and fluorine, is particularly suitable.
It is understood that membranes with similar properties such as NeoseptaTM CM-l, NeoseptaTM CMS, NeoseptaTM ACS, ~eoseptaTM
CLE~E and IonacTM MC 3470, are suitable, and that the use of combinations of other membranes may yield the desired results~
The alternating cation and anion membranes form a number of alternating diluate compartments and concentrate compartments which are situated between the anode compartment and the cathode compartment. The anode and cathode are made of suitable materials. For example, the anode can be made of platinum-coated titanium and the cathode of stainless steel.
The cathode can also be advantageously made of a material for which the hydrogen overvoltage is lowered, such as platinum-coated titanium, in order to favour hydrogen evolution over the deposition of metal. A source of direct current is connected to the electrodes.
The metal sulfate-containing solution, preferably free of suspended solids, is fed as feed solution to the diluate compartments. A depleted solution or diluate, i.e. a treated metal sulfate solution, is withdrawn from the diluate compartments. A concentrate, i.e. a solution concentrated in monovalent ions, is withdrawn from the concentrate compartments, preferably at a rate equal to the rate of the net water transfer from the diluate to the concentrate during the electrodialysis. It is important to maintain turbulent conditions in the concentrate and diluate compartments. This can be achieved by passing solution through the compartments at a sufficient rate. Preferably, at least a portion of the diluate and at least a portion of the concentrate are circulated to the diluate and concentrate compartments respectively, mainly to ensure turbulent conditions, but also to achieve the desired removal and concentration of monovalent ions. The feed solution is conveniently added to the portion of circulating diluate. A portion of the circulating diluate is withdrawn as treated metal sulfate-containing solution having a reduced content of monovalent ions. A portion of the circulating concentrate is also withdrawn. The withdrawn treated solution and the withdrawn concentrate may be treated further, if desired and as will be described.
During electrodiilysis, water transport occurs by osmosis and electro-osmosis usually in opposing directions and at different rates. The net water transport generally occurs in the direction from the diluate to the concentrate compartments. This water transport is sufficient, in most cases, to form concentrate stream flows adequate for withdrawal. In those cases wherein the net water transfer rate to the concentrate compartments is less than the desired withdrawal rate of concentrate from the concentrate compartments, it will be necessary to feed a receiving solution to the concentrate compartments. For example, the receiving solution, compatible with the general operation of the electrodialysis unit, may be chosen from water, dilute sulfuric acid and a dilute salt solution such as, for example, a dilute sodium sulfate solution.
In the cathode and anode compartments the predominant reactions are hydrogen and oxygen evolution, respectively.
However, small amounts of metal may deposit on the cathode.
The deposition may be controlled by arranging the membranes in the electrodialysis unit such that anion permselective membranes form the end membranes, i.e., are the membranes next to the electrode compartments; selecting a large enough electrode rinse flow at a controlled pH to minimize the concentration of metal ions; or by using a cathode made of a suitable material to promote the evolution of hydrogen over metal deposition, such as, for example, a cathode material of platinum-coated titanium.
The cathode and the anode compartments are rinsed separately or with a common rinse solution circulated to both the electrode compartments. The rinse solution may be chosen from dilute sulfuric acid and, preferably, sulfuric acid-sodium sulfate solution maintained at a pH in the range of about 0 to 4, values in the higher end of the range being preferred for more efficient fluoride removal. A portion of the rinse solution may be removed from circulation and be replaced with a substantially equal portion of fresh solution so that the metal concentration in the rinse solution is maintained at about 150 mg/L or less.
During electrodialysis, the monovalent cations and anions in the metal sulfate-containing feed solution pass from the diluate compartments to the concentrate compartments through 15 20;~354~;
the monovalent permselective cation and anion membranes respectively, leaving substantially all multivalent cations and anions in the diluate compartments. In the embodiment for the selective removal of monovalent anions, the monovalent anions pass from the diluate to the concentrate compartments through the monovalent anion permselective membranes, leaving monovalent cations and substantially leaving the multivalent ions in the diluate compartments. The gases evolved at the electrodes are carried from the cathode and anode compartments in the rinse solution. Both embodiment may be used for the removal of monovalent anions from metal sulfate solutions.
In those solutions wherein the metal is sodium or potassium, the monovalent anions are effectively removed. As the sodium or potassium is usually present in such solutions in a high concentration, a portion of the monovalent cations is also removed with the concentrate that contains the removed anions.
The concentration of the metals in the concentrate may be reduced, as will be described.
The electrodialysis unit may be operated with solution temperatures in the range of from just above the freezing temperature of the solution to as high as about 60C, i.e.
from about 0C to 60C, preferably from about 20C to 50C.
The method is conducted with a metal sulfate-containing feed solution that has a pH controlled at values that do not cause undesirable reactions such as, for example, precipitation of metal as hydroxide or basic metal sulfate. The pH values 16 X0335~5 depend on the metals present in the feed solution, especially the dominant metal. &enerally, the pH values are in ranges between values from about one to about nine. Specifically, for effective removal of monovalent cations and, especially the monovalent anions, the pH of a copper sulfate-containing solution should be maintained in the range of about 1 to 5.5, preferably 3 to 5; for a cadmium sulfate-containing solution in the range of about 1 to 5.5, preferably 2.5 to 5; for a nickel or cobalt sulfate-containing solution in the range of about 1 to 6, preferably 4 to 5; for a ferrous iron sulfate-containing solution in the range of about 1 to 6, preferably 4 to 6; for a manganese sulfate-containing solution in the range of about 1 to 7, preferably 4 to 7; for a magnesium sulfate-containing solution in the range of about 1 to 7, preferably 4 to 6.5; and for a sodium or potassium sulfate-containing solution in the range of about 1 to 9, preferably 4 to 8. We have also found that the removal of anions of fluorine is especially sensitive to the pH due to the formation of hydrogen fluoride ions at a pH below about 3.5.
For effective fluoride removal, the pH of the diluate and concentrate streams containing fluoride is, therefore, preferably at a value of not less than about 2 and, to enhance fluoride removal, most preferably at a value in the range of about 3.5 to 9, depending on the metals in the feed.
The flow rate of solutions through the concentrate and diluate compartments should be such that the linear velocity is sufficient to obtain turbulent flow. The flows of solutions 17 X033~45 through the concentrate and diluate compartments and the anode and cathode compartments should be substantially balanced in order to maintain a differential pressure across the membranes that does not exceed about 150 kPa and is preferably in the range of from 0 kPa to about 50 kPa.
Feed rates to the electrodialysis unit may be selected in the range of about 2 L/h.m2 to 60 L/h.m2 per membrane pair, the selected value being dependent on the monovalent ion concentrations in the metal sulfate-containing solution and the value of the current density.
The process can be operated with a current applied to the electrodes such that the equivalent membrane current density (applied current per effective membrane surface area) is in the range of about 10 A/m2 to 500 A/m2. Below about 10 A/m2, the ionic transfer rate is too low, while above about 500 A/m2 the rate of replenishing monovalent ions at the membrane diffusion layer is too low, with resulting water splitting and/or loss of permselectivity. Water splitting and permselectivity loss are substantially obviated when operating with current densities in the preferred range of about 50 A/m2 to 300 A/m2.
Although electrodialysis may be effective in one stage to reduce concentrations of monovalent ions to the desired low concentrations or to substantially zero, it may be desirable to have more than one stage of electrodialysis. In more than 2(1335~5 one stage, the stages are preferably connected in series, diluate withdrawn from one stage being fed to the diluate compartments of a subsequent stage whereby concentrations of monovalent ions may be further reduced to the desired level.
Using one or more stages, the anions of chlorine, bromine and fluorine may be substantially completely removed so that the treated solution is substantially free of chloride, fluoride and bromide.
If desired, the concentra~e may be further concentrated by electrodialysis. Concentrate withdrawn from concentrate compartments from the first stage electrodialysis is fed to the diluate compartments of a second stage. Such a step may be advantageous to reduce loss of metal with the concentrate, as concentrate is usually discarded after treatment as an effluent. Diluate from such a second electrodialysis of concentrate may be returned as feed to the first stage electrodialysis. Reduction of loss of metal may be particularly desirable when solutions of, for example, sodium or potassium sulfate are treated for the removal of halides.
By a judicious selection of the size of the electrodialysis unit or the use of a staged process, the method may be used for the effective control of concentrations of monovalent ions in the treated solutions. Thus, the concentration of the monovalent ions is controlled in one or more stages and treated solution having the desired concentration is recovered. If the concentration of monovalent ions is below ZC~33S~S
the desired value, the desired monovalent ions may be added to attain the desired value.
If needed, the membranes may be cleaned periodically to remove any deposits such as of calcium sulfate or fluoride, ma~nesium fluoride, or basic metal sulfates. The membranes may be cleaned physically or chemically with a suitable acid solution such as, for example, a 15% solution of acetic acid, a 2 M hydrochloric acid or dilute sulfuric acid followed by adequate rinsing with water. ~he electrodes may be cleaned with dilute sulfuric acid.
The invention will now be illustrated by means of the following non-limitative examples. The apparatus used in the tests described in the examples consisted of an electrodialysis unit having ten membrane pairs with a total effective membrane area of 1720 cm2. The unit was of the so-called sheet flow design (liquid flows in a sheet-like fashion in a relatively straight line from the inlet to the exit ports), and anionic membranes were employed adjacent the electrode compartments.
The cation permselective membranes were SelemionTM CMR
membranes, and the anion permselective membranes were SelemionTM ASR membranes. The cathode was made of stainless steel, and the anode was made of platinum coated titanium.
In all tests, diluate was circulated through the diluate compartments of the unit at a velocity of from 5 to 7 cm/s, 20 Z03354~
and concentrate was circulated through the concentrate compartments of the unit at a velocity of from 3 to 6 cm/s.
Feed solution was added to the circulating diluate.
Example 1 A predominantly copper sulfate-containing solution, containing 43 g/L Cu, 9 g/L Ni, 1.2 g/L Zn, 1.2 g/L Fe, 0.245 g/L Cl, 0.131 g/L F, 0.300 g/L Br, 0.380 g/L Na and 0.100 g/L K, was subjected to electrodialysis in the electrodialysis unit. The solution was fed at a rate of 14 L/h.m2. A current was applied between the electrodes to give a current density of 100 A/m2. The temperature was maintained at 40C. The electrode compartments were rinsed with a rinse solution containing 5 g/L Na2SO4, maintained at a pH of 2.0 + 0.1, and circulated at a rate of 50 L/h.m2. The unit was operated for 24 hours. The circulating diluate was controlled at a pH in the preferred range of 3 to 5.
The final diluate solution was analyzed and was found to contain 43 g/L Cu, 9.2 g/L Ni, 1.2 g/L Zn, 1.2 g/L Fe, 0.038 g/L F, 0.210 g/L Na, 0.040 g/L K, no Cl, Br was below the detection limit. The final concentrate solution was analyzed, and was found to contain 2.4 g/L Cl, 2.2 g/L Br, 0.930 g/L F, 1.60 g/L Na and 0.38 g/L K (bromide analysis was carried out with an ion chromatography interference apparatus). As can be seen from the results, the chloride and bromide were completely removed from the copper sulfate solution, while the removal of fluoride was 72%. The fluoride removal is more efficient than usually obtained when a predominantly zinc ulfate-containing solution containing a similar amount of fluoride is treated.
Example_2 A predominantly magnesium sulfate-containing solution, containing 105 g/L MgSO4.7 H2O, 1.155 g/L Cl and 0.300 g/L Br, was subjected to electrodialysis in the electrodialysis unit.
The solution was fed at a rate of 8.75 L/h.m2. ~he current applied between the electrodes gave a current density of 100 A/m2. The temperature was maintained at 39C. The electrode compartments were rinsed with a rinse solution containing 5 g/L Na2SO4~ maintained at a pH of 2.0 + 0.1, and circulated at a rate of 50 L/h.m2. The unit was operated for 8 hours. The circulating diluate was maintained during operation at a pH
value in the preferred range of 4 to 6.5.
After the operation was completed the diluate and concentrate were analy~ed. The diluate was found to contain 95 g/L
MgSO4.7H2O, 0.087 g/L Cl and Br below the detection limit.
The concentrate was found to contain 135 g/L MgSO4.7H2O, 4.1 g/L Cl and 2.1 g/L Br.
The high magnesium content of the concentrate suggests the possible transfer of monovalent complexed anionic magnesium species.
203~S45 The results show that the anions of chlorine and bromine were effectively removed from the feed solution recovered as diluate.
ExamPle 3 A predominantly cadmium sulfate-containing solution, containing 37 g/L Cd, 7.4 g/L Zn, 5.3 g/L Ni, 3.6 g/L Fe, 5.2 g/L Cu, 0.346 g/L Mg, 0.091 g/L Mn, 0.2 g/L Cl, 0.2 g/L Br, 0.063 g/L F, 0.90 g/L Na, 0.22 g/L K and 0.030 g/L Tl, was fed at a rate of 8.75 L/h.m2. The current density was 100 A/m2.
The temperature was maintained at 38C. The electrode compartments were rinsed with a rinse solution containing 5 g/L Na2SO4 maintained at a pH of 2.0 + 0.1, and circulated at a rate of 50 L/h.m2. The solution was fed to the unit for 8 hours. During operation, the pH of the circulating diluate was maintained in the preferred range of 2.5 to 5.
After operation was completed, the diluate and the concentrate were analyzed. The diluate was found to contain 35 g/L Cd, 7.0 g/L Zn, 5.0 g/L Ni, 3.4 g/L Fe, 4.9 g/L Cu, 0.326 g/L Mg, 0.086 g/L Mn, 0 g/L Cl, 0.0195 g/L F, Br was below the detection limit, 0.40 g/L Na, 0.15 g/L K and 0.017 g/L Tl.
The concentrate was found to contain 42 g/L Cd, 8.4 g/L Zn, 5.9 g/L Ni, 4.1 g/L Fe, 5.9 g/L Cu, 0.397 g/L Mg, 0.102 g/L
Mn, 5.9 g/L Cl, 0.560 g/L Br, 0.175 g/L F, 1.5 g/L Na, 0.2 g/L
K and 0.063 g/L Tl. The results show that the halides and thallium were effectively removed from the feed solution. The ~033SA5 metal losses to the concentrate were relatively high. The metal losses may be minimized by using a two-stage process.
Example 4 A predominantly sodium sulfate-containing solution, containing 16.3 g/L Na, 0.040 g/L K, 2.120 g/L Cl, 0.110 g/L F and 0.100 g/L Br, was treated for the removal of halides. The feed rate of the solution was 28 L/h.m2. The current density was 200 A/mZ, and the solution was fed to the unit for a period of 8 hours. The electrode compartments were rinsed with feed solution maintained at a pH of 2.0 + 0.1 at a rate of 10 L/h.m2. The pH of the circulating diluate was maintained in the preferred range of from 4 to 8.
The recovered diluate was analyzed and found to contain 13 g/L
Na, 0.028 g/L K, 0.450 g/L Cl, 0.040 g/L F and Br below the detection limit.
The recovered concentrate was analyzed and found to contain 35 g/L Na, 0.120 g/L K, 13.8 g/L Cl, 0.600 g/L F and 0.590 g/L
Br.
The test results show that halides may be effectively removed from a sodium and potassium sulfate solution. The metal content of the concentrate may be reduced by subjecting the concentrate to a second stage electrodialysis.
The results of the above examples show that monovalent anions and cations may be effectively removed from metal sulfate-containing solutions containing a metal chosen from copper, nickel, manganese, iron, magnesium, cadmium, sodium and potassium, one of these metals being present in a dominant amount. ~he results also show that anions of chlorine, and bromine may be substantially removed from metal sulfate-containing solution, and that halides may be effectively removed from monovalent cation-containing solutions.
It is understood that changes and modifications may be made in the embodiments of the invention without departing from the scope and purview of the appended claims.
METAL SULFATE SOLUTIONS BY ELECTRODIALYSIS
This invention relates to the removal of monovalent ions from metal sulfate solutions by electrodialysis.
BACKGROUND OF THE INVENTION
Most hydrometallurgical processes for the recovery of metals in a sulfate system involve the formation and treatment of metal sulfate solutions and may include e]ectrowinning, solvent extraction or electrorefining. These processes may encounter problems with the presence of monovalent ions, especially halides such as chloride, fluoride and bromide, or cations such as sodium, potassium and thallium. Such monovalent ions may be naturally present in the ore or concentrate or may be added during the processing of the ore or concentrate. For example, small amounts of chloride, usually in the form of sodium chloride, may be added to obtain a good quality copper or to control the presence of silver.
In many cases it will be important to control the amount of monovalent ions, especially halides, in recirculating solutions, particularly in processes for producing high-purity metals. In many of these processes, a removal step may be required or is actually a step in the process. For example, according to US 4 338 168, copper concentrates are leached with a chloride and bromide-containing solutionl and solution is subsequently purified by adding copper to remove the halides. This process has the disadvantage of requiring the addition of copper for halide removal. According to US 4 698 139, base metals that include Cu, Co, Ni, Mn, Mg, Zn and Fe are electrolytically recovered from materials containing chloride and fluoride. The materials are leached, metal sulfates are crystallized, the crystals are washed with return acid, then leached in water, and metal is recovered by electrolysis. The halides are removed from the crystallization mother liquor by evaporation. The disadvantages of this process include the inclusion of halides in the crystallized sulfates and the formation of halides by evaporation. According to US 4 874 436, a high-purity copper is electrolytically deposited in a diaphragm cell from a nitric acid electrolyte also containing silver. Chloride is added to precipitate silver, and after the removal of silver, the solution is recirculated to the cell. This process will require the careful control of chloride addition and concentration to prevent the deleterious effects of chloride in the cell. It must also be noted that it is important to control the halide content of electrolytes used in electrolytic processes to avoid anode scaling, erosion and undesirable halogen generation. Other disadvantages of the various halide removal processes or steps include the often incomplete removal of the halides requiring additional removal steps, and high costs.
In other processes it may also be necessary to control the content of halides or to remove halides to avoid their harmful effects on processes and equipment. Such processes may include the treatment or recovery of sodium or potassium sulfate, especially when the pure salts are desired.
The removal of ions from solutions could be carried out by methods that may include electrodialysis, which is well documented. The removal of monovalent ions from zinc sulfate electrolyte by electrodialysis has been patented by the same assignee as of the present invention (US Patent 4 715 939).
Neither this reference nor the other references, however, disclose the use of electrodialysis in purification of metal sulfate-containing solutions for the recovery of metal other than zinc, or the removal by electrodialysis of monovalent ions such as ions of chlorine, bromine, fluorine, sodium, potassium and thallium from metal sulfate solutions containing metals other than zinc.
SUMMARY OF THE INVENTION
We have now found that the halides as well as monovalent cations can be efficiently removed from metal sulfate solutions containing dominant metal other than zinc by electrodialysis.
According to the invention, metal sulfate-containing solution containing at least one metal other than zinc, and containing monovalent ions, is treated by passing solutions through an electrodialysis unit to remove both monovalent anions and monovalent cations or monovalent anions alone. The method of the invention may also be successfully used for the removal of monovalent anions from solutions that contain monovalent cations such as sodium and potassium. Preferably, the metal other than zinc is chosen from the group consisting of Cu, Co, Ni, Mn, Fe, Mg, Cd Na and K. A metal of this group may be present in a dominant amount with other metals of this group being present in lesser amounts. The electrodialysis unit includes a number of alternating concentrate and diluate compartments separated by alternating cationic and anionic membranes, and an anode and a cathode compartment containing an anode and a cathode, respectively. The anionic and cationic membranes are selected from suitable monovalent ion permselective membranes for the removal of both monovalent anions and cations. When selective removal of monovalent anions is desired and removal of monovalent cations is not required, monovalent anion permselective membranes are used, and the cationic membranes are selected from the generally available cationic membranes. Metal sulfate-containing solution is passed through the diluate cells and the current applied to the electrodes causes monovalent ions to pass from the diluate compartments through the membranes into the concentrate in the concentrate compartments. Any metal deposition on the electrodes is controlled by one or more of a number of means that include the controlling of the compositions and flow rate of an electrode rinse solution that is circulated through the anode and the cathode compartmentsi the arranging of the alternating membranes such that the anode compartment and cathode compartment are separated from the adjacent diluate or concentrate compartments by a monovalent 5 ,~033~4~
anion permselective membrane; and the use of a cathode material that favours hydrogen evolution over metal deposition. Because halide, especially fluoride, removal is pH dependent, the pH of the electrolyte is carefully controlled within predetermined ranges. The range is dependent on the solution being treated, usually on what metal is dominant. Generally, values of the pH are in the range of about one to nine. A less strict control of pH is required when the anion removal is restricted to anions of chlorine or bromine or both. The electrodialysis may be carried out in one or more stages depending on the concentration of monovalent ions in the metal sulfate solutions to be treated and/or the desired level of these ions and the metal ions in the treated solutions. ~y choosing appropriate conditions, the method of the invention can result in the effective removal in one or more stages of 90~ or better of the monovalent ions, especially the ions of chlorine, bromine, fluorine, sodium, potassium and thallium from the rnetal sulfate solutions. In many cases, anions of chlorine, fluorine and bromine may be substantially completely removed.
The content of the monovalent ions in treated solutions may be readily controlled in the process or in the treated solution.
According to the invention, there is provided a method for the treatment by electrodialysis of metal sulfate-containing solution containing at least one metal other than zinc and containing concentrations of monovalent ions including at least one ion chosen from the group consisting of cations of thallium, sodium and potassium, and of anions of chlorine, bromine and fluorine, said method comprising the steps of feeding metal sulfate-containing solution to diluate compartments of an electrodialysis unit comprising a multiplicity of alternating monovalent cation permselective exchange membranes and monovalent anion permselective exchange membranes, said membranes defining alternating diluate and concentrate compartments, an anode compartment and a cathode compartment, an anode positioned in the anode compartment and a cathode positioned in the cathode compartment; applying an electrical current between the anode and the cathode at a value such that the value of the corresponding current density is in the range of about 10 A/m2 to 500 A/m2; feeding metal sulfate-containing solution at a controlled pH having a value in ranges between values from about 1 to about 9 to said diluate compartments; circulating flows of diluate and concentrate through the diluate and concentrate compartments, respectively, at a linear velocity sufficient to maintain turbulent flow in said compartments; withdrawing at least a portion of the circulating diluate as the treated metal sulfate-containing solution with reduced concentrations of said monov~lent ions; and withdrawing at least a portion of the circulating concentrate.
According to a second embodiment, there is provided a method for the treatment by electrodialysis of metal sulfate-containing solution containing at least one metal other than 7 2~3354~
zinc and containing concentrations of monovalent anions including at least one anion chosen from the group consisting of anions of chlorine, bromine and fluorine, said method comprising the steps of feeding metal sulfate-containing solution to diluate compartments of an electrodialysis unit comprising a multiplicity of alternating cation exchange membranes and monovalent anion permselective exchange membranes, said membranes defining alternating diluate and concentrate compartments, an anode compartment and a cathode compartment, an anode positioned in the anode compartment and a cathode positioned in the cathode compartment; applying an electrical current between the anode and the cathode at a value such that the value of the corresponding current density is in the range of about 10 A/m2 to 500 A/m2; feeding metal sulfate-containing solution at a controlled pH having value in ranges between values from about 1 to about 9 to said dilute compartments; circulating flows of diluate and concentrate through the diluate and concentrate compartments, respectively, at a linear velocity sufficient to maintain turbulent ~low in said compartments; withdrawing at least a portion of the circulating diluate as the treated metal sulfate-containing solution with reduced concentrations of monovalent anions; and withdrawing at least a portiGn of the circulating concentrate.
Preferably, the at least one metal other than zinc is chosen from the group consisting of copper, cobalt, nickel, manganese, iron, magnesium, cadmium, sodium and potassium.
8 Z~33~45 Preferably, one Gf the metals of this group is present in a dominant amount in the metal sulfate-containing solution.
It is an aspect of the present invention to provide a method for the removal of monovalent ions from metal sulfate-containing solutions containing metal other than zinc.
It is another aspect to provide a method for the removal of both monovalent cations and monovalent anions from metal sulfate-containing solutions containing metal other than zinc by electrodialysis.
It is a further aspect to provide a method for the selective removal of monovalent anions from metal sulfate-containing solutions containing metal other than æinc by electrodialysis.
It is yet another aspect to provide a method for treating metal sulfate-containing solution by electrodialysis for the removal of monovalent ions and controlling the concentration of the monovalent ions in treated solution.
These and other aspects of the present invention will become apparent from the following detailed description of the method of the present invention.
DETAILED DES~RIPTION
Metal sulfate solutions that may be treated according to the method of the present invention include solutions obtained from or present in the treating of metal-containing materials such as ores, concentrates and metallurgical process intermediate products with sulfuric acidl or solutions used 9 ~ 354S
for extracting metal by electrolytic or solvent extraction processes. Metal sulfate solutions treated also include solutions encountered in the processing of magnesium, sodium and potassium salts. The metal sulfate solutions contain at least one metal other than zinc. The at least one metal other than zinc may be present in a dominant amount and is, preferably, chosen from the group consisting of Cu, Co, Ni, Mn, Fe, Mg, Cd, Na and K. The metal sulfate solutions may also contain other metals that may accompany the preferred metal in the sulfate solutions such as, for example, arsenic, antimony, zinc, lead, bismuth, silver, tin and calcium, as well as the metals of above-recited group present in amounts smaller than the amount of the metal that i5 dominant in the solutions. The metal sulfate solutions include monovalent ions comprising at least one monovalent cation or at least one monovalent anion. Thus, for example, the metal sulfate solution containing monovalent ions may be a copper sulfate-containing solution wherein copper is the dominant metal, and other metals such as zinc, arsenic, iron, silver, nickel and other metals may be present in ionic form. The metal sulfate solutions are subjected to a treatment to remove monovalent anions such as the anions of chlorine, bromine, fluorine, and monovalent cations such as the cations of sodium, potassium and thallium. Any nitrate, if present in solution, will be removed with the other monovalent ions. As will be explained hereinafter, only monovalent anions may be selectively removed or both monovalent anions and cations may be removed. As will be explained, the method may also be used to remove monovalent 10 ;~033~4~
anions from ~etal solutions wherein the metal is a monovalent ion such as sodium or potassium.
Metal sulfate-containing solution, present in a process wherein such solution occurs or is treated, is fed to an electrodialysis unit. The electrodialysis unit comprises a multiplicity of vertically arranged, alternating monovalent anion permselective exchange membranes and cation exchange membranes or monovalent cation permselective exchange membranes, a cathode compartment and an anode compartment.
The choice of membranes is important. When only monovalent anions are to be removed, the use of a combination of monovalent anion permselective membranes and general cation exchange membranes (limited permselectivity for mono over multivalent cations) makes it possible to remove monovalent anions selectively from the solution. This combination of membranes can be advantageously used when monovalent cations are present in small amounts. When both monovalent anions and monovalent cations are to be removed, a combination of monovalent anion and monovalent cation permselective membranes is used. Such combination will, therefore, make it possible to separate monovalent ions from multivalent ions, and to concentrate the monovalent cations and the monovalent anions.
The metal sulfate-containing solution thereby becomes depleted in these ions.
We have found that suitable monovalent cation permselective membranes are, for example, strongly acidic membranes which 11 ~(3;~35~5 have a membrane matrix of a styrene di-vinyl benzene co-polymer on a polyvinyl chloride base and possess sulfonic acid radicals (R-SO3H3 as active groups. The active groups comprise 3-4 milli-equivalents per gram of dry resin which is satisfactory to provide the desired selectivity for monovalent ions. Suitable monovalent cation permselective membranes are specially treated SelemionTM CMV, SelemionTM Experimental A
(specially treated on one face), and Selemion1-M Experimental B or SelemionTM CSR (both surfaces specially treated) and specially treated SelemionTM CMR. If the object is to remove only monovalent anions such as anions of chlorine, bromine and fluorine, and not monovalent cations, the choice of the cation membrane can be extended to include others available on the market such as, for example, those with sulfonic acid radicals (R -SO3 H) as the active groups at 3-5 milli-equivalents per gram of dry resin, e.g., SelemionTM CMV.
Suitable monovalent anion permselective membranes are, for example, strongly basic membranes with quaternary ammonium active groups, such as, for example, derived from trimethylamine (for example, R-N(CH2)3.Cl)l at 3-4 milli-equivalents per gram of dry resin, and having a matrix of a styrene di-vinyl benzene co-polymer on a polyvinyl chloride base. SelemionTM ASV, ASS or ASR, which is permselective for monovalent anions, particularly anions of chlorine, bromine and fluorine, is particularly suitable.
It is understood that membranes with similar properties such as NeoseptaTM CM-l, NeoseptaTM CMS, NeoseptaTM ACS, ~eoseptaTM
CLE~E and IonacTM MC 3470, are suitable, and that the use of combinations of other membranes may yield the desired results~
The alternating cation and anion membranes form a number of alternating diluate compartments and concentrate compartments which are situated between the anode compartment and the cathode compartment. The anode and cathode are made of suitable materials. For example, the anode can be made of platinum-coated titanium and the cathode of stainless steel.
The cathode can also be advantageously made of a material for which the hydrogen overvoltage is lowered, such as platinum-coated titanium, in order to favour hydrogen evolution over the deposition of metal. A source of direct current is connected to the electrodes.
The metal sulfate-containing solution, preferably free of suspended solids, is fed as feed solution to the diluate compartments. A depleted solution or diluate, i.e. a treated metal sulfate solution, is withdrawn from the diluate compartments. A concentrate, i.e. a solution concentrated in monovalent ions, is withdrawn from the concentrate compartments, preferably at a rate equal to the rate of the net water transfer from the diluate to the concentrate during the electrodialysis. It is important to maintain turbulent conditions in the concentrate and diluate compartments. This can be achieved by passing solution through the compartments at a sufficient rate. Preferably, at least a portion of the diluate and at least a portion of the concentrate are circulated to the diluate and concentrate compartments respectively, mainly to ensure turbulent conditions, but also to achieve the desired removal and concentration of monovalent ions. The feed solution is conveniently added to the portion of circulating diluate. A portion of the circulating diluate is withdrawn as treated metal sulfate-containing solution having a reduced content of monovalent ions. A portion of the circulating concentrate is also withdrawn. The withdrawn treated solution and the withdrawn concentrate may be treated further, if desired and as will be described.
During electrodiilysis, water transport occurs by osmosis and electro-osmosis usually in opposing directions and at different rates. The net water transport generally occurs in the direction from the diluate to the concentrate compartments. This water transport is sufficient, in most cases, to form concentrate stream flows adequate for withdrawal. In those cases wherein the net water transfer rate to the concentrate compartments is less than the desired withdrawal rate of concentrate from the concentrate compartments, it will be necessary to feed a receiving solution to the concentrate compartments. For example, the receiving solution, compatible with the general operation of the electrodialysis unit, may be chosen from water, dilute sulfuric acid and a dilute salt solution such as, for example, a dilute sodium sulfate solution.
In the cathode and anode compartments the predominant reactions are hydrogen and oxygen evolution, respectively.
However, small amounts of metal may deposit on the cathode.
The deposition may be controlled by arranging the membranes in the electrodialysis unit such that anion permselective membranes form the end membranes, i.e., are the membranes next to the electrode compartments; selecting a large enough electrode rinse flow at a controlled pH to minimize the concentration of metal ions; or by using a cathode made of a suitable material to promote the evolution of hydrogen over metal deposition, such as, for example, a cathode material of platinum-coated titanium.
The cathode and the anode compartments are rinsed separately or with a common rinse solution circulated to both the electrode compartments. The rinse solution may be chosen from dilute sulfuric acid and, preferably, sulfuric acid-sodium sulfate solution maintained at a pH in the range of about 0 to 4, values in the higher end of the range being preferred for more efficient fluoride removal. A portion of the rinse solution may be removed from circulation and be replaced with a substantially equal portion of fresh solution so that the metal concentration in the rinse solution is maintained at about 150 mg/L or less.
During electrodialysis, the monovalent cations and anions in the metal sulfate-containing feed solution pass from the diluate compartments to the concentrate compartments through 15 20;~354~;
the monovalent permselective cation and anion membranes respectively, leaving substantially all multivalent cations and anions in the diluate compartments. In the embodiment for the selective removal of monovalent anions, the monovalent anions pass from the diluate to the concentrate compartments through the monovalent anion permselective membranes, leaving monovalent cations and substantially leaving the multivalent ions in the diluate compartments. The gases evolved at the electrodes are carried from the cathode and anode compartments in the rinse solution. Both embodiment may be used for the removal of monovalent anions from metal sulfate solutions.
In those solutions wherein the metal is sodium or potassium, the monovalent anions are effectively removed. As the sodium or potassium is usually present in such solutions in a high concentration, a portion of the monovalent cations is also removed with the concentrate that contains the removed anions.
The concentration of the metals in the concentrate may be reduced, as will be described.
The electrodialysis unit may be operated with solution temperatures in the range of from just above the freezing temperature of the solution to as high as about 60C, i.e.
from about 0C to 60C, preferably from about 20C to 50C.
The method is conducted with a metal sulfate-containing feed solution that has a pH controlled at values that do not cause undesirable reactions such as, for example, precipitation of metal as hydroxide or basic metal sulfate. The pH values 16 X0335~5 depend on the metals present in the feed solution, especially the dominant metal. &enerally, the pH values are in ranges between values from about one to about nine. Specifically, for effective removal of monovalent cations and, especially the monovalent anions, the pH of a copper sulfate-containing solution should be maintained in the range of about 1 to 5.5, preferably 3 to 5; for a cadmium sulfate-containing solution in the range of about 1 to 5.5, preferably 2.5 to 5; for a nickel or cobalt sulfate-containing solution in the range of about 1 to 6, preferably 4 to 5; for a ferrous iron sulfate-containing solution in the range of about 1 to 6, preferably 4 to 6; for a manganese sulfate-containing solution in the range of about 1 to 7, preferably 4 to 7; for a magnesium sulfate-containing solution in the range of about 1 to 7, preferably 4 to 6.5; and for a sodium or potassium sulfate-containing solution in the range of about 1 to 9, preferably 4 to 8. We have also found that the removal of anions of fluorine is especially sensitive to the pH due to the formation of hydrogen fluoride ions at a pH below about 3.5.
For effective fluoride removal, the pH of the diluate and concentrate streams containing fluoride is, therefore, preferably at a value of not less than about 2 and, to enhance fluoride removal, most preferably at a value in the range of about 3.5 to 9, depending on the metals in the feed.
The flow rate of solutions through the concentrate and diluate compartments should be such that the linear velocity is sufficient to obtain turbulent flow. The flows of solutions 17 X033~45 through the concentrate and diluate compartments and the anode and cathode compartments should be substantially balanced in order to maintain a differential pressure across the membranes that does not exceed about 150 kPa and is preferably in the range of from 0 kPa to about 50 kPa.
Feed rates to the electrodialysis unit may be selected in the range of about 2 L/h.m2 to 60 L/h.m2 per membrane pair, the selected value being dependent on the monovalent ion concentrations in the metal sulfate-containing solution and the value of the current density.
The process can be operated with a current applied to the electrodes such that the equivalent membrane current density (applied current per effective membrane surface area) is in the range of about 10 A/m2 to 500 A/m2. Below about 10 A/m2, the ionic transfer rate is too low, while above about 500 A/m2 the rate of replenishing monovalent ions at the membrane diffusion layer is too low, with resulting water splitting and/or loss of permselectivity. Water splitting and permselectivity loss are substantially obviated when operating with current densities in the preferred range of about 50 A/m2 to 300 A/m2.
Although electrodialysis may be effective in one stage to reduce concentrations of monovalent ions to the desired low concentrations or to substantially zero, it may be desirable to have more than one stage of electrodialysis. In more than 2(1335~5 one stage, the stages are preferably connected in series, diluate withdrawn from one stage being fed to the diluate compartments of a subsequent stage whereby concentrations of monovalent ions may be further reduced to the desired level.
Using one or more stages, the anions of chlorine, bromine and fluorine may be substantially completely removed so that the treated solution is substantially free of chloride, fluoride and bromide.
If desired, the concentra~e may be further concentrated by electrodialysis. Concentrate withdrawn from concentrate compartments from the first stage electrodialysis is fed to the diluate compartments of a second stage. Such a step may be advantageous to reduce loss of metal with the concentrate, as concentrate is usually discarded after treatment as an effluent. Diluate from such a second electrodialysis of concentrate may be returned as feed to the first stage electrodialysis. Reduction of loss of metal may be particularly desirable when solutions of, for example, sodium or potassium sulfate are treated for the removal of halides.
By a judicious selection of the size of the electrodialysis unit or the use of a staged process, the method may be used for the effective control of concentrations of monovalent ions in the treated solutions. Thus, the concentration of the monovalent ions is controlled in one or more stages and treated solution having the desired concentration is recovered. If the concentration of monovalent ions is below ZC~33S~S
the desired value, the desired monovalent ions may be added to attain the desired value.
If needed, the membranes may be cleaned periodically to remove any deposits such as of calcium sulfate or fluoride, ma~nesium fluoride, or basic metal sulfates. The membranes may be cleaned physically or chemically with a suitable acid solution such as, for example, a 15% solution of acetic acid, a 2 M hydrochloric acid or dilute sulfuric acid followed by adequate rinsing with water. ~he electrodes may be cleaned with dilute sulfuric acid.
The invention will now be illustrated by means of the following non-limitative examples. The apparatus used in the tests described in the examples consisted of an electrodialysis unit having ten membrane pairs with a total effective membrane area of 1720 cm2. The unit was of the so-called sheet flow design (liquid flows in a sheet-like fashion in a relatively straight line from the inlet to the exit ports), and anionic membranes were employed adjacent the electrode compartments.
The cation permselective membranes were SelemionTM CMR
membranes, and the anion permselective membranes were SelemionTM ASR membranes. The cathode was made of stainless steel, and the anode was made of platinum coated titanium.
In all tests, diluate was circulated through the diluate compartments of the unit at a velocity of from 5 to 7 cm/s, 20 Z03354~
and concentrate was circulated through the concentrate compartments of the unit at a velocity of from 3 to 6 cm/s.
Feed solution was added to the circulating diluate.
Example 1 A predominantly copper sulfate-containing solution, containing 43 g/L Cu, 9 g/L Ni, 1.2 g/L Zn, 1.2 g/L Fe, 0.245 g/L Cl, 0.131 g/L F, 0.300 g/L Br, 0.380 g/L Na and 0.100 g/L K, was subjected to electrodialysis in the electrodialysis unit. The solution was fed at a rate of 14 L/h.m2. A current was applied between the electrodes to give a current density of 100 A/m2. The temperature was maintained at 40C. The electrode compartments were rinsed with a rinse solution containing 5 g/L Na2SO4, maintained at a pH of 2.0 + 0.1, and circulated at a rate of 50 L/h.m2. The unit was operated for 24 hours. The circulating diluate was controlled at a pH in the preferred range of 3 to 5.
The final diluate solution was analyzed and was found to contain 43 g/L Cu, 9.2 g/L Ni, 1.2 g/L Zn, 1.2 g/L Fe, 0.038 g/L F, 0.210 g/L Na, 0.040 g/L K, no Cl, Br was below the detection limit. The final concentrate solution was analyzed, and was found to contain 2.4 g/L Cl, 2.2 g/L Br, 0.930 g/L F, 1.60 g/L Na and 0.38 g/L K (bromide analysis was carried out with an ion chromatography interference apparatus). As can be seen from the results, the chloride and bromide were completely removed from the copper sulfate solution, while the removal of fluoride was 72%. The fluoride removal is more efficient than usually obtained when a predominantly zinc ulfate-containing solution containing a similar amount of fluoride is treated.
Example_2 A predominantly magnesium sulfate-containing solution, containing 105 g/L MgSO4.7 H2O, 1.155 g/L Cl and 0.300 g/L Br, was subjected to electrodialysis in the electrodialysis unit.
The solution was fed at a rate of 8.75 L/h.m2. ~he current applied between the electrodes gave a current density of 100 A/m2. The temperature was maintained at 39C. The electrode compartments were rinsed with a rinse solution containing 5 g/L Na2SO4~ maintained at a pH of 2.0 + 0.1, and circulated at a rate of 50 L/h.m2. The unit was operated for 8 hours. The circulating diluate was maintained during operation at a pH
value in the preferred range of 4 to 6.5.
After the operation was completed the diluate and concentrate were analy~ed. The diluate was found to contain 95 g/L
MgSO4.7H2O, 0.087 g/L Cl and Br below the detection limit.
The concentrate was found to contain 135 g/L MgSO4.7H2O, 4.1 g/L Cl and 2.1 g/L Br.
The high magnesium content of the concentrate suggests the possible transfer of monovalent complexed anionic magnesium species.
203~S45 The results show that the anions of chlorine and bromine were effectively removed from the feed solution recovered as diluate.
ExamPle 3 A predominantly cadmium sulfate-containing solution, containing 37 g/L Cd, 7.4 g/L Zn, 5.3 g/L Ni, 3.6 g/L Fe, 5.2 g/L Cu, 0.346 g/L Mg, 0.091 g/L Mn, 0.2 g/L Cl, 0.2 g/L Br, 0.063 g/L F, 0.90 g/L Na, 0.22 g/L K and 0.030 g/L Tl, was fed at a rate of 8.75 L/h.m2. The current density was 100 A/m2.
The temperature was maintained at 38C. The electrode compartments were rinsed with a rinse solution containing 5 g/L Na2SO4 maintained at a pH of 2.0 + 0.1, and circulated at a rate of 50 L/h.m2. The solution was fed to the unit for 8 hours. During operation, the pH of the circulating diluate was maintained in the preferred range of 2.5 to 5.
After operation was completed, the diluate and the concentrate were analyzed. The diluate was found to contain 35 g/L Cd, 7.0 g/L Zn, 5.0 g/L Ni, 3.4 g/L Fe, 4.9 g/L Cu, 0.326 g/L Mg, 0.086 g/L Mn, 0 g/L Cl, 0.0195 g/L F, Br was below the detection limit, 0.40 g/L Na, 0.15 g/L K and 0.017 g/L Tl.
The concentrate was found to contain 42 g/L Cd, 8.4 g/L Zn, 5.9 g/L Ni, 4.1 g/L Fe, 5.9 g/L Cu, 0.397 g/L Mg, 0.102 g/L
Mn, 5.9 g/L Cl, 0.560 g/L Br, 0.175 g/L F, 1.5 g/L Na, 0.2 g/L
K and 0.063 g/L Tl. The results show that the halides and thallium were effectively removed from the feed solution. The ~033SA5 metal losses to the concentrate were relatively high. The metal losses may be minimized by using a two-stage process.
Example 4 A predominantly sodium sulfate-containing solution, containing 16.3 g/L Na, 0.040 g/L K, 2.120 g/L Cl, 0.110 g/L F and 0.100 g/L Br, was treated for the removal of halides. The feed rate of the solution was 28 L/h.m2. The current density was 200 A/mZ, and the solution was fed to the unit for a period of 8 hours. The electrode compartments were rinsed with feed solution maintained at a pH of 2.0 + 0.1 at a rate of 10 L/h.m2. The pH of the circulating diluate was maintained in the preferred range of from 4 to 8.
The recovered diluate was analyzed and found to contain 13 g/L
Na, 0.028 g/L K, 0.450 g/L Cl, 0.040 g/L F and Br below the detection limit.
The recovered concentrate was analyzed and found to contain 35 g/L Na, 0.120 g/L K, 13.8 g/L Cl, 0.600 g/L F and 0.590 g/L
Br.
The test results show that halides may be effectively removed from a sodium and potassium sulfate solution. The metal content of the concentrate may be reduced by subjecting the concentrate to a second stage electrodialysis.
The results of the above examples show that monovalent anions and cations may be effectively removed from metal sulfate-containing solutions containing a metal chosen from copper, nickel, manganese, iron, magnesium, cadmium, sodium and potassium, one of these metals being present in a dominant amount. ~he results also show that anions of chlorine, and bromine may be substantially removed from metal sulfate-containing solution, and that halides may be effectively removed from monovalent cation-containing solutions.
It is understood that changes and modifications may be made in the embodiments of the invention without departing from the scope and purview of the appended claims.
Claims (15)
1. A method for the treatment by electrodialysis of metal sulfate-containing solution containing at least one metal other than zinc and containing concentrations of monovalent ions including at least one ion chosen from the group consisting of cations of thallium, sodium and potassium and of anions of chlorine, bromine and fluorine, said method comprising the steps of feeding metal sulfate-containing solution to diluate compartments of an electrodialysis unit comprising a multiplicity of alternating monovalent cation permselective exchange membranes and monovalent anion permselective exchange membranes, said membranes defining alternating diluate and concentrate compartments, an anode compartment and a cathode compartment, an anode positioned in the anode compartment and a cathode positioned in the cathode compartment; applying an electrical current between the anode and the cathode at a value such that the value of the corresponding current density is in the range of about 10 A/m2 to 500 A/m2; feeding metal sulfate-containing solution at a controlled pH having a value in ranges between values from about 1 to about 9 to said diluate compartments; circulating flows of diluate and concentrate through the diluate and concentrate compartments, respectively, at a linear velocity sufficient to maintain turbulent flow in said compartments; withdrawing at least a portion of the circulating diluate as the treated metal sulfate-containing solution with reduced concentrations of said monovalent ions; and withdrawing at least a portion of the circulating concentrate.
2. A method as claimed in claim 1, wherein said at least one metal other than zinc is chosen from the group consisting of copper, cobalt, nickel, manganese, iron, magnesium, cadmium, sodium and potassium.
3. A method for the treatment by electrodialysis of metal sulfate-containing solution containing at least one metal other than zinc and containing concentrations of monovalent anions including at least one anion chosen from the group consisting of anions of chlorine, bromine and fluorine, said method comprising the steps of feeding metal sulfate-containing solution to diluate compartments of an electrodialysis unit comprising a multiplicity of alternating cation exchange membranes and monovalent anion permselective exchange membranes, said membranes defining alternating diluate and concentrate compartments, an anode compartment and a cathode compartment, an anode positioned in the anode compartment and a cathode positioned in the cathode compartment;
applying an electrical current between the anode and the cathode at a value such that the value of the corresponding current density is in the range of 10 A/m2 to 500 A/m2; feeding metal sulfate-containing solution at a controlled pH having a value in ranges between values from about 1 to about 9 to said diluate compartments;
circulating flows of diluate and concentrate through the diluate and concentrate compartments, respectively, at a linear velocity sufficient to maintain turbulent flow in said compartments; withdrawing at least a portion of the circulating diluate as the treated metal sulfate-containing solution with reduced concentrations of monovalent anions; and withdrawing at least a portion of the circulating concentrate.
applying an electrical current between the anode and the cathode at a value such that the value of the corresponding current density is in the range of 10 A/m2 to 500 A/m2; feeding metal sulfate-containing solution at a controlled pH having a value in ranges between values from about 1 to about 9 to said diluate compartments;
circulating flows of diluate and concentrate through the diluate and concentrate compartments, respectively, at a linear velocity sufficient to maintain turbulent flow in said compartments; withdrawing at least a portion of the circulating diluate as the treated metal sulfate-containing solution with reduced concentrations of monovalent anions; and withdrawing at least a portion of the circulating concentrate.
4. A method as claimed in claim 3, wherein said at least one metal other than zinc is chosen from the group consisting of copper, cobalt, nickel, manganese, iron, magnesium, cadmium, sodium and potassium.
5. A method as claimed in claim 1, 2, 3 or 4, wherein said electrodialysis is carried out in more than one stage by feeding the withdrawn portion of said circulating diluate from one stage to diluate compartments of a subsequent stage whereby concentrations of monovalent ions are further reduced.
6. A method as claimed in claim 1, 2, 3 or 4, wherein said electrodialysis is carried out in two stages by feeding the withdrawn portion of said circulating concentrate from one stage to diluate compartments of a second state whereby loss of metal in concentrate is reduced.
7. A method as claimed in claim 1, wherein said metal sulfate-containing solution contains at least one metal other than zinc chosen from the group consisting of copper, cobalt, nickel, manganese, iron, magnesium, cadmium, sodium and potassium, said metal sulfate-containing solution has a pH at a value in the range of about 1 to about 9 and is fed to said diluate compartments at rates in the range of about 2 L/h.m2 to L/h.m2 per membrane pair; said membranes have a membrane matrix of a styrene di-vinyl benzene copolymer and have active groups in an amount in the range of about 3 to 4 milli-equivalents per gram of dry resin, the active groups of the monovalent cation permselective exchange membranes being sulfonic groups and the active groups of the monovalent anion permselective membranes being a quaternary ammonium groups derived from trimethylamine; said anode compartment and said cathode compartment are rinsed with a circulating rinse solution of sodium sulfate containing sodium sulfate in a concentration in the range of about 0.1 M to 1.0 M, said rinse solution being maintained at a value of the pH in the range of about 0 to 4; said electrical current is applied such that the value of the corresponding current density is in the range of about 50 A/m2 to 300 A/m2; the temperature in the unit is maintained in the range of about 0°C to 60°C; and said flows of solutions are passed through the diluate and concentrate compartments and said rinse solution is circulated through said anode compartment and said cathode compartment at flow rates such that the differential pressure across the membranes is less than 150 kPa.
8. A method as claimed in claim 3, wherein said metal sulfate-containing solution contains at least one metal other than zinc chosen from the group consisting of copper, cobalt, nickel, manganese, iron, magnesium, cadmium, sodium and potassium, said metal sulfate-containing solution has a pH at a value in the range of about 1 to about 9 and is fed to said diluate compartments at rates in the range of about 2 L/h.m2 to L/h.m2 per membrane pair; said cation exchange membranes have a membrane matrix of a styrene di-vinyl benzene copolymer and have sulfonic active groups in an amount in the range of about 3 to 5 milli-equivalents per gram of dry resin, said monovalent anion permselective exchange membranes have a membrane matrix of styrene di-vinyl benzene copolymer and have active groups of quaternary ammonium groups derived from trimethylamine;
said anode compartment and said cathode compartment are rinsed with a circulating rinse solution of sodium sulfate containing sodium sulfate in a concentration in the range of about 0.1 M to 1.0 M, said rinse solution being maintained at a value of the pH in the range of about 0 to 4; said electrical current is applied such that the value of the corresponding current density is in the range of about 50 A/m2 to 300 A/m2; the temperature in the unit is maintained in the range of about 0°C to 60°C; and said flows of solutions are passed through the diluate and concentrate compartments and said rinse solution is circulated through said anode compartment and said cathode compartment at flow rates such that the differential pressure across the membranes is less than 150 kPa.
said anode compartment and said cathode compartment are rinsed with a circulating rinse solution of sodium sulfate containing sodium sulfate in a concentration in the range of about 0.1 M to 1.0 M, said rinse solution being maintained at a value of the pH in the range of about 0 to 4; said electrical current is applied such that the value of the corresponding current density is in the range of about 50 A/m2 to 300 A/m2; the temperature in the unit is maintained in the range of about 0°C to 60°C; and said flows of solutions are passed through the diluate and concentrate compartments and said rinse solution is circulated through said anode compartment and said cathode compartment at flow rates such that the differential pressure across the membranes is less than 150 kPa.
9. A method as claimed in claim 1, 3, 7 or 8, wherein one metal in said metal sulfate-containing solution is present in a dominant amount and is chosen from the group consisting of copper, cobalt, nickel, manganese, iron, magnesium, cadmium, sodium and potassium.
10. A method as claimed in claim 1, 3, 7 or 8, wherein said metal sulfate-containing solution comprises monovalent ions of chlorine and bromine and said monovalent ions of chlorine and bromine are substantially completely removed from said metal sulfate-containing solution.
11. A method as claimed in claim 5, wherein said metal sulfate-containing solution comprises monovalent ions of chlorine, bromine and fluorine and said monovalent ions of chlorine, bromine and fluorine are substantially completely removed from said metal sulfate-containing solution.
12. A method as claimed in claim 2 or 4, wherein said controlled pH has a value for copper sulfate-containing solution in the range of about 1 to 5.5, for cadmium sulfate-containing solution in the range of about 1 to 5.5, for nickel sulfate-containing solution in the range of about 1 to 6, for cobalt sulfate-containing solution in the range of about 1 to 6, for ferrous iron sulfate containing solution in the range of about 1 to 6, for manganese sulfate-containing solution in the range of about 1 to 7, for magnesium sulfate-containing solution in the range of about 1 to 7, for sodium sulfate containing solution in the range of about 1 to 9, and for potassium sulfate-containing solution in the range of about 1 to 9.
13. A method as claimed in claim 2 or 4, wherein said controlled pH has a value for copper sulfate-containing solution in the range of about 3 to 5, for cadmium sulfate-containing solution in the range of about 2.5 to 5, for nickel sulfate-containing solution in the range of about 4 to 5, for cobalt sulfate-containing solution in the range of about 4 to 5, for ferrous iron sulfate containing solution in the range of about 4 to 6, for manganese sulfate-containing solution in the range of about 4 to 7, for magnesium sulfate-containing solution in the range of about 4 to 6.5, for sodium sulfate containing solution in the range of about 4 to 8, and for potassium sulfate-containing solution in the range of about 4 to 8.
14. A method as claimed in claim 9, wherein said controlled pH has a value for copper sulfate-containing solution in the range of about 1 to 5.5, for cadmium sulfate-containing solution in the range of about 1 to 5.5, for nickel sulfate-containing solution in the range of about 1 to 6, for cobalt sulfate-containing solution in the range of about 1 to 6, for ferrous iron sulfate containing solution in the range of about 1 to 6, for manganese sulfate-containing solution in the range of about 1 to 7, for magnesium sulfate-containing solution in the range of about 1 to 7, for sodium sulfate containing solution in the range of about 1 to 9, and for potassium sulfate-containing solution in the range of about 1 to 9.
15. A method as claimed in claim 9, wherein said controlled pH has a value for copper sulfate-containing solution in the range of about 3 to 5, for cadmium sulfate-containing solution in the range of about 2.5 to 5, for nickel sulfate-containing solution in the range of about 4 to 5, for cobalt sulfate-containing solution in the range of about 4 to 5, for ferrous iron sulfate containing solution in the range of about 4 to 6, for manganese sulfate-containing solution in the range of about 4 to 7, for magnesium sulfate-containing solution in the range of about 4 to 6.5, for sodium sulfate containing solution in the range of about 4 to 8, and for potassium sulfate-containing solution in the range of about 4 to 8.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2033545 CA2033545A1 (en) | 1991-01-03 | 1991-01-03 | Method for the removal of monovalent ions from metal sulfate solutions |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2033545 CA2033545A1 (en) | 1991-01-03 | 1991-01-03 | Method for the removal of monovalent ions from metal sulfate solutions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2033545A1 true CA2033545A1 (en) | 1992-07-04 |
Family
ID=4146752
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2033545 Abandoned CA2033545A1 (en) | 1991-01-03 | 1991-01-03 | Method for the removal of monovalent ions from metal sulfate solutions |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2033545A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013026093A1 (en) * | 2011-08-22 | 2013-02-28 | Newamu Ip Holdings Pty Ltd | Method for the treatment of acidic leach liquors |
| CN110787640A (en) * | 2019-11-04 | 2020-02-14 | 陕西省膜分离技术研究院有限公司 | Separation method of Rb + and Na + based on ionic liquid polymer liquid membrane |
| CN112996755A (en) * | 2018-11-01 | 2021-06-18 | 苏特沃克技术有限公司 | System and method for removing monovalent anionic species from wastewater |
-
1991
- 1991-01-03 CA CA 2033545 patent/CA2033545A1/en not_active Abandoned
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013026093A1 (en) * | 2011-08-22 | 2013-02-28 | Newamu Ip Holdings Pty Ltd | Method for the treatment of acidic leach liquors |
| CN112996755A (en) * | 2018-11-01 | 2021-06-18 | 苏特沃克技术有限公司 | System and method for removing monovalent anionic species from wastewater |
| CN110787640A (en) * | 2019-11-04 | 2020-02-14 | 陕西省膜分离技术研究院有限公司 | Separation method of Rb + and Na + based on ionic liquid polymer liquid membrane |
| CN110787640B (en) * | 2019-11-04 | 2021-11-23 | 陕西省膜分离技术研究院有限公司 | Liquid film pair Rb based on ionic liquid polymer+And Na+Of (2) a separation method |
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