JPH0386295A - Method for reducing amount of negative ion metal-ligand complex om solution - Google Patents

Abstract

PURPOSE: To efficiently remove an anionic metal-ligand complex in a soln. by allowing the soln. to contact with a calcined matter of a compd. expressed by a specified general formula or their mixture, then separating the calcined matter, etc., from the soln.

CONSTITUTION: A material selected among a compd. expressed by formula A_wB_x(OH)_yC_z.nH₂O (A is a bivalent metal cation, B is a tervalent metal cation, C is a univalent to quadrivalent anion, 0≤z≤x≤4≤w≤1/2y, 12≥n≥3/2x), the calcined matter of the compd. or their mixture is brought into contact with the soln. Then the amount of the anionic metal-ligand complex in the soln. is reduced by separating the compd. expressed by the formula from the soln.. There is a natural or synthetic hydrotalcite, pyroaurite, etc., as suitable example of the compd. expressed by the formula.

COPYRIGHT: (C)1991,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for reducing the amount of anionic metal-ligand complexes in solution. Furthermore, the present invention also provides metal-
A method for removing ligand complexes to make wastewater more environmentally acceptable.

Specifically, the present invention provides metal-cyanate complexes, metal-thiocyanate complexes, metal-thiosulfate complexes, metal-citrate complexes and/or metal-ethylenediaminetetraacetic acid (EDTA).
) A method for removing substantially all of one or more complexes from a solution containing the complexes.

BACKGROUND OF THE INVENTION Cyanides have been used for many years in industries such as metal electroplating, electroless plating and recovery of precious metals from ores. As a result of such industrial applications, significant amounts of wastewater containing metal-cyanate complexes or their associated cyanate or thiocyanate ionic species complexes are generated every day. That is, gold mining alone accounts for a large proportion of contaminated wastewater streams.

During this time, several methods have been proposed to remove metal-cyanide complexes from industrial solutions. Although these methods are feasible, they typically have high operating costs, complex equipment requirements, or require careful treatment control of a type that is typically not possible in remote mines or in many water treatment facilities. There are significant practical or commercial disadvantages, such as the need to U.S. Pat. No. 4,092,154 discloses a method for precipitating noble metal ions from a solution containing metal-cyanide ions. The process proceeds by adding to the solution a mixture of aluminum powder and a reducing agent selected from alkali metal hydrosulphites, alkali metal borohydrides and hydrazine.

On the other hand, in U.S. Pat. No. 4,537,686, waste liquid is treated with an oxygen-containing gas, a copper catalyst, and a reagent selected from S02 and an alkali or alkaline earth metal, sulfite or bisulfite. Methods are taught to reduce the total cyanide content in aqueous effluents by treating at a pH of 5-12.

The silver complexes found in most photographic processing solutions are known to exist as stable, soluble silver-thiosulfate complexes. This complex is produced by the reaction of silver bromide and ammonium thiosulfate during photographic development. The most commonly used methods for removing silver-thiosulfate complexes from solutions include (a) chemical displacement cartridge methods in which silver displaces iron when the solution is passed through stainless wool; and (b) conventional methods. An example is the ion exchange resin method.

U.S. Pat. No. 4,394,354 further teaches that activated carbon impregnated with at least about 0.1% by weight halogen acts as a suitable silver ion scavenger. Also, according to U.S. Pat. No. 4,396,585, impregnating non-carbon adsorbents such as natural or basal zeolites, activated alumina, activated silica, Fuller's earth, bentonite clay, and hectorite clay with halogens. A similar improvement can also be made by

Recently, the removal of silver from wastewater streams has become important for health and environmental reasons. The subsequent recovery of precious metals is also gaining economic importance. Silver in ionic form is described in U.S. Pat. No. 4,026.784, 4.1.
It is well known that it can be recovered from photographic processing solutions by electrolytic methods as disclosed in U.S. Pat. -For boat fishing,
Since it is very difficult to reduce silver concentrations to less than about 500 ppm by electrolysis, the above recovery method
It was used only for solutions containing concentrations above 0 ppm. Other disadvantages of these methods include their expense and the need for continuous monitoring of the system.

Citric acid and ethylenediaminetetraacetic acid (EDTA) are
It has been used as a chelating agent for many years in metal electroplating and electroless plating, and in various wood or pulp treatments.
and has been used as a scale remover/inhibitor for equipment cleaning. As a result, metal-citric acid complex and metal-
Such chelating agents and chelators are used for BDT octaplex.
or is often present in large amounts in wastewater from industries that use the ligand. Metal-citric acid complexes are also present in rainwater flows in areas where large amounts of citric acid are precipitated in the soil. Some known methods for removing and recovering such various metal complexes from solutions include Bnviron-+nentalP.
rogress, Volume 3, No. 2, pp. 124-128 (
1984), SFearot
) etc. “Recovery Process fo
r Complexed CopFer-Bearin
g R1n5e Wate16+. The article also describes the shortcomings associated with each recovery method. Also, U.S. Pat. No. 4,157.
No. 434 discloses a method for removing metal-EDTA complexes from polyphenylene ether resin solutions. In this method, a solution is brought into contact with alumina to remove the metal.
Selectively adsorbs EDTA.

A primary object of the present invention is to provide an improved method for reducing the amount of anionic metal-ligand complexes in solution. Furthermore, it is an object of the present invention to remove environmentally unacceptable amounts of one or more anionic metal-complexes (or chelates).
The object of the present invention is to provide an efficient method for treating solutions containing .

In a preferred embodiment of the present invention, the amount of metal-cyanate complex, metal-thiocyanate complex, metal-thiosulfate complex, metal-citrate complex and/or metal-EDTA complex in the aqueous solution is measured on a metal ion basis. less than about 1 ppm or about 0.
It can even be reduced to less than 1 ppm.

Furthermore, it is an object of the present invention to provide solutions containing one or more metal complexes, including metal-cyanate complexes, metal-thiocyanate complexes, metal-thiosulfate complexes, metal-citrate complexes and/or metal-EDTA complexes. An object of the present invention is to provide a method for removing substantially all metal complexes from metal complexes. Furthermore, it is an object of the present invention to provide a simple method for removing metal-ligand complexes from a solution, which proceeds by adding the complex-adsorbing material to the solution or passing the solution through a container containing the complex-adsorbing material. The purpose is to provide a method. Furthermore, it is an object of the present invention to convert wastewater streams such as photographic processing solutions, metal electroplating and electroless plating solutions, mining and ore recovery solutions, etc. essentially from hydrotalcite, calcined hydrotalcite or mixtures thereof. The object of the present invention is to provide a method for removing chelates from wastewater streams by simply contacting them with a complex adsorbent.

Furthermore, it is an object of the present invention to provide a method for adsorbing metal-ligand complexes that is stable and effective in the alkaline pH range, where adsorption of anions is generally difficult. Furthermore, it is an object of the present invention to provide a process for treating wastewater which prevents the generation of significant quantities of environmentally unacceptable by-products. The complex-containing materials of preferred embodiments of the invention produce little or no leaching of metal complexes (or other toxic substances) over extended periods of time.

Furthermore, it is an object of the present invention to provide a method for reducing metal complexes, which does not require any special equipment, regardless of the mine location or in industrial scale water treatment plants. Furthermore, it is an object of the present invention to overcome the problems and drawbacks of other processing methods mentioned above.

[Means for solving the problem, examples, and effects]

In order to achieve the objects of the invention set forth above and other advantages that will become apparent from the detailed description of the preferred embodiments below, a method is provided for reducing the amount of anionic metal-ligand complexes in solution. Ru. In the method of the present invention, first, a solution is
Formula AwBx (OH) yCs '' IIH20 (wherein ^ represents a divalent metal cation, B represents a trivalent metal cation, C represents a monovalent to tetravalent anion, W, X.

ySz and n are 0≦2≦×≦4≦w≦1/2y and 12
≧n≧372x), a calcined product of this compound, or a mixture thereof. The complex-saturated or complex-containing material is then separated from the purified solution. In a preferred embodiment, the compound contacted with the solution is natural or synthetic hydrotalcite, pyroolite or tachovite (
takovite). Most preferably, the complex-containing solution is contacted with sufficient calcined hydrotalcite to remove substantially all of the metal complexes.

Furthermore, according to the invention, metal-cyanide complexes, metal-thiocyanate complexes, metal-thiosulfate complexes are removed from photographic processing solutions, metal electroplating and electroless plating solutions, mining and ore recovery solutions or other wastewater streams. , a method for removing substantially all of the metal-citric acid complex and/or metal-EDTAI is provided. The method includes contacting the solution with a sufficient amount of a complex adsorbent material consisting essentially of a compound selected from hydrotalcite, calcined hydrotalcite, and mixtures thereof.

Further features, other objects and advantages of the invention will become more apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

In the detailed description of the preferred embodiments set forth below, a sufficient amount of a compound selected from hydrotalcite, calcined hydrotalcite, or mixtures thereof is used to remove metal-ligand complexes or chelates from wastewater. Although reference is made repeatedly to adsorption, the invention can be practiced with other compounds belonging to the same family. The system is 2A, ,B, (
DH) yC, ・nH2O (wherein, ^ represents a divalent metal cation, B represents a trivalent metal cation, C represents a monovalent to tetravalent anion, and ' s xSV ts z and n meet the following conditions or The formula is 0≦z≦x≦4≦w≦1/2y and 12≧n
≧3/2X). A preferred embodiment of this same family of compounds has the formula ^1182(DH) +gC4H,0 (wherein ^
are Mg+2, N l + 2, Fe+1 and l n +
2, and B is ^l"
3.11" e+3 and Cr+3, where C is preferably OH-, Cl-,
Br-, NOs-CHaCOO-, CO3-3, so,
-'', PO, -3, Fe (CN) s-' and Fe
(CN) is an anion selected from the group consisting of s-'). In some literature, all compounds satisfying the above formula are collectively referred to as "hydrotalcite." In other cases, this family of compounds is classified into various groups depending on the divalent and trivalent cations that constitute every other layer of the complex adsorption structure. For example, pyro-oleite has the basic formula Mg5Fe2OH+gCOa'
4H20 (such compounds are also called "shogrenite").

On the other hand, Takobaite is 2N1gAl2OH+5COa・
Consisting essentially of compounds having 4H20. However, in the following portion of the detailed description of the present invention, for convenience, only representative hydrotalcite-type compounds will be used to describe the metal-
Selective removal of ligand complexes will be explained.

In this specification, "hydrotalcite" refers to 2Mgg
^12 (DH) l 6CD3・4H20 or a rewritten formula 6Mg0・^1203 ・CO2・12
It means any natural or synthetic compound that satisfies H and O. In its ionic form, hydrotalcite (Mg
gAl2(OH)+s:l ”・(co,)−”・4H
It seems like 20.

The main structural unit of hydrotalcite is fundamentally bluestone, namely magnesium hydroxide CMg(OH)2
:] is that. More specifically, the hydrotalcite structure consists of a sheet of magnesium hydroxide octahedra with a Mg ion in the center of a number of (OH) ions sharing adjacent edges. By replacing a portion of the divalent magnesium ions with trivalent aluminum cations, a layer of magnesium and aluminum components is created that still maintains the basic sheet-like structure of bluestone.

To compensate for the resulting charge imbalance, additional anions C are inserted between the Mg-Al layers and into this sheet-like structure. Due to the formation of hydrogen bonds, the anion C and water molecules form an intermediate layer of (C-nH2O) between the bluestone-like layers. The anion with the greatest affinity for binding to discipline such hydrotalcite interlayers is the carbonate ion (co, -2).

The steric distribution of carbonate ions in the hydrotalcite interlayer is
Part of this depends on how the AI+3 substitution ion is located within the bluestone. Therefore, water molecules surrounding carbonate ions play the role of "void filler". The spacing between bluestone layers also correlates with the amount or degree of aluminum replacement to the structure. Specifically, as the aluminum substitution increases, the interlayer spacing decreases due to the increased electrostatic attraction between the positive hydroxide layer and the negative interlayer. The thickness of the interlayer will also vary depending on the size and orientation of the various anions that may replace some or all of the carbonate ions within the hydrotalcite interlayer structure.

This compound, hydrotalcite, exists in both natural and pedestal forms. Natural hydrotalcite deposits are found in Snarum, Norway and the Ural Mountains. Hydrotalcite typically exists in the form of serpentine, talcum schist, or in some cases as an alteration product of spinel, where hydrotalcite forms as a superior product of spinel. Like most minerals and compounds, natural hydrotalcite is virtually impossible to find in its pure state. Natural deposits generally contain one or more other minerals including, but not limited to, bennine and muscovite or a combination of undesirable heavy metal ions. In the prior art, it is virtually impossible to remove all such incidental elements and impurities from natural hydrotalcite. In any case, known deposits of natural hydrotalcite remain very limited.

Several methods are known to produce synthetic hydrotalcite with higher purity. Such compounds can be made into fine powders, -
20 mesh neck grains or 1/8 inch diameter (3,175 m
It can be manufactured in the form of extrudates etc. of m).

No. 3,539,306 discloses that an aluminum component selected from aluminum hydroxide, aluminum-amino acid salts, aluminum alcoholades, water-soluble aluminates, aluminum nitrate, and aluminum sulfate is maintained at a pH of 8 or above. A magnesium component selected from magnesium oxide, magnesium hydroxide and water-soluble magnesium salts and a carbonate ion-containing compound are mixed in an aqueous medium. The resulting hydrotalc product is used as an antacid.

Other known methods for synthesizing hydrotalcite include the pyrolysis of dry ice or ammonium carbonate from (a) a mixture of magnesium oxide and alpha-alumina or (b) a mixture of magnesium nitrate and aluminum nitrate. and then bring the system to about 325°F (163°C).
temperature below 2.000 psi (141 kg/cm'
) and 20,000 psi (1410 kg/cm2). however,
Such methods are impractical for producing hydrotalcite on an industrial scale due to the use of high pressures. The use of such high pressures also produces compounds other than hydrotalcite. Compounds other than hydrotalcite include bruceite, boehmite, diaspore, and hydromagnesite. Yet another method for producing synthetic hydrotalcite is described by “ProFerties
of a SynthetlcMagnesium-＾
1uminum (:arbonate Hydrox
ide andits Re1ation6Bip t
o Magnesium-AlumtnumDoub
le Hydroxide Manasseite,
and Hydrotalcite”.

The American Minelogist
, Vol. 52, pp. 1036-1047 (1967). In this paper, Ross et al. described a mixed solution of MgCl2 and AlCl3 as
A method for producing hydrotalcite by titration with NaOH in a carbon dioxide-free system is described. The suspension is then dialyzed for 30 days at 60°C to produce hydrated Mg-Al carbonate hydroxide with both manasseite and hydrotalcite properties.

In a preferred embodiment of the invention, the improved adsorption process comprises contacting a wastewater stream, effluent or other complex contaminated solution with a material consisting essentially of calcined hydrotalcite. "Consisting essentially of" means that the substance is 85 or 90%
more preferably more than about 95% or 98% hydrotalcite in calcined (or activated) form. It is understood, however, that physical methods are not so thorough as to be able to remove all traces of incidental elements and impurities from materials that may be considered suitable for use as adsorbents in accordance with the present invention. Should. In the dehydrated state, calcined hydrotalcite is 2Mg5AIJs (DH)2
It seems to be similar to the product with .

Heat treatment of natural or synthetic hydrotalcite generally results in a metal-complex adsorbent that is superior to the untreated material.

Such heat treatment can be carried out with conventional heating media or with recently developed heating media maintained at one or more temperatures of approximately 400-650°C, although any lower temperature of 300°C may be sufficient. unknown. Although the preferred activation temperature, which is between about 400 and 450°C, tends to maximize the surface area and pore volume of the adsorbent, heating to temperatures above 800°C adversely affects the total adsorption properties of calcined hydrotalcite. seems to be the case.

Thermal activation of hydrotalcite results in a porous skeletal structure from which water and carbonate ions are partially, if not entirely, excluded. The resulting adsorbent has an average pore size of approximately 55 pores, with approximately 170 pores of any size. The skeleton (or solid component) density of this calcined material is approximately 2.9 g/cm'
and its total pore volume is approximately 0.3 cm" 7 g.

When calcined, the specific surface area of hydrotalcite as measured by the BBT nitrogen adsorption method varies from about 20 m"7 g to about 50-200 m
m” increases to 7g.

In one aspect of the invention, a method of treating a solution containing an environmentally unacceptable amount of one or more anionic metal-ligand complexes comprises: (a) the formula A6B2 (OH) + s
C・4H20 (in the formula, ^ is Mg + 2, N l + 2,
is selected from the group consisting of Fe + 2 and Zn + 2, B is selected from the group consisting of AI", Fe + 3 and Cr + 3, and C is DH-, Cdo, Br, NO3-1CH3COO -co, -2, so
,-'', POa-3, Fe(CN)s-' and Fe(C
(b) the solution has a metal complex content of less than about 1 ppm, more preferably about 0, as measured on a metal ion basis; ．． contacting the compound in an amount sufficient to reduce the concentration to less than 1 ppm.

More preferably, the method further comprises heating the compound at about 400-650° C. before contacting with the solution in step (b) above.
calcination at one or more temperatures between. or,
Optionally, the method of the invention may further involve separating the complex saturated compounds from the solution using known or recently developed separation means.

In another embodiment, a method for removing substantially all of a metal-ligand complex from a solution containing the complex comprises contacting the solution with one of the complex adsorption materials described above, and then comprising:
It involves separating the substance from its solution. Preferably, only material saturated (or fully loaded) with complex should be removed from solution, while undesirable levels of complex should remain. Once the complex content of the solution has been sufficiently reduced, the remainder of the unused material can be separated from the solution for later use.

In a preferred embodiment, the method described above comprises: - boat fishing;
It is carried out by adding powdered calcined hydrotalcite directly to the solution to be treated.

The amount of powder to add is determined by testing a representative sample of the solution.
It can be predetermined externally by determining the amount of adsorbent required to remove substantially all of the complex. The saturated material can then be removed from this solution by one or more known or recently developed techniques, including filtration, gravity sedimentation, and centrifugation.

Alternatively, hydrotalcite can be used before or after calcination.
It can be mixed with one or more binder materials, extruded, shaped or shaped into larger particles, including granules and the like. These large particles are then placed in a column, fluidized bed or other device in which the contents are stratified through which the solution is passed. In any case, the present invention basically proceeds almost independently of the pH and/or temperature of the reaction system.

The pH of almost all solutions to which calcined hydrotalcite is added will be sufficiently basic for complex adsorption to occur.

If the pH of the solution remains below about 4 after the addition of hydrotalcite, complex adsorption according to the present invention will likely not proceed. However, such conditions only exist in acidic solutions with high buffering capacity. The metal-ligand complex can be removed from the solution according to the invention at one or more temperatures between room temperature and the boiling point of the solution. In a preferred embodiment, such metal complexes have about 6
Further removal may be achieved at temperatures below 50°C; higher temperatures may increase adsorption and/or total adsorption efficiency.

The method of the present invention also reduces the amount of complexes in wastewater containing one or more of the following: metal-cyanate complexes, metal-thiocyanate complexes, metal-thiosulfate complexes, metal-citrate complexes, and metal-EDTA complexes. It can also be used to make the wastewater more environmentally acceptable by reducing the . In particular, the present invention reduces the complex content of photoprocessing, metal electroplating, electroless plating, mining and ore recovery fluids and other waste streams to less than about 1 ppm, preferably about 0.5.0 ppm.
3 or O, less than 1 ppm, most preferably about 50 ppb
It can be reduced to below (measured on metal ion basis).

The substance adsorbing the complex becomes itself environmentally acceptable. This means that, according to the present invention, the entire metal complex is chemically and physically adsorbed into the interior of said material rather than on its structure, and harmful or toxic complexes are removed from bluestone or other environmentally acceptable materials. This means that it is effectively encapsulated between stable layers. Unless dissolved in an acidic solution with a pH of less than about 4 or 5, it is impossible to leach unacceptable levels of toxic metal complexes from the rehydrated structure as explained below. The saturated material remains environmentally safe.

The method described above is characterized in that the metal of the complex is selected from silver, gold, barium, calcium, cadmium, copper, iron, magnesium, manganese, nickel, lead, palladium, platinum, radium, rhodium, tin, strontium, vanadium and zinc. Particularly suitable for removing metal-ligand complexes. The chelating agent, chelator or ligand (hereinafter referred to as "ligand") of the complex to be removed consists of cyanide ions, thiocyanate ions, thiosulfate ions, citrate ions and ethylenediaminetetraacetic acid (EDTA). can be selected from the group. However, it should be understood that both groups described above are merely representative and the invention is not limited to the removal of only these complexing substances. In fact, other ligands that can be adsorbed according to the invention include nitrilotriacetic acid (NTA), ) lance-1,2-cyclohexadiaminetetraacetic acid (cy-DT
A), diethylenetriaminepentaacetic acid (DTPA), )lyethylenetetraaminehexaacetic acid (TTHA), glycol ether diaminetetraacetic acid (GBTA) and iminoniacetic acid (ID8).

Specific examples of metal complexes (or chelates) that can be removed from solution include Au(CN)2- and Ag(S2Dj).
- Noble metal-cyan complex or noble metal-thiosulfate complex such as [or 8g (S20.) 2-3), Cu-Ni and/or
Or zinc-citric acid. Furthermore, by carrying out the present invention, it is also possible to reduce the metal-[EDT content in the solution. The metal in this case is preferably selected from silver, calcium, copper, iron, magnesium, nickel and zinc.

- For boat fishing, the present invention provides that the calcined hydrotalcite is capable of adsorbing metal-ligand complexes that are divalent, trivalent, or more than tetravalent, although to a lesser extent monovalent complexes can also be adsorbed. It is more suitable for adsorbing.

Without being limited to any theory of operation, preferred embodiments of the present invention! It is believed that Mr. S progresses according to the following mechanism. Upon calcination (or activation), both carbonate ions and water are expelled from the basic hydrotalcite structure according to the equation below.

450℃ MgJlz (DH) l 11CO3・4H20→
MggAIJs (OH) a+CO□ +llH2
O The calcined hydrotalcite is then contacted with a complex-containing solution, whereby the complex occupies the vacant anion position within the adsorbent structure by rehydration. Through such physical adsorption, approximately 75-90% and 100% of the theoretical maximum adsorption capacity can be obtained.
The adsorption capacity of the complex adsorbent material is even possible. The above mechanism also explains why the present invention should proceed in an environment substantially free of carbon dioxide or carbonates.

Because thermal activation displaces the carbonate ions of these compounds from the hydrotalcite, calcined hydrotalcite-type products exhibit greater affinity for carbonate before adsorbing most other anions. Re-adsorbs ions.

Each of the accompanying figures shows an adsorption isomixture showing the adsorption capacity of hydrotalcite or activated hydrotalcite for various typical metal-ligand complexes. For each of the exemplified complexes, substantially all of the metal-ligands could be adsorbed by adding the respective amount of complex adsorbent material. However, some complexes were more easily adsorbed than others.

In the graph of Figure 1a, the y-axis represents various amounts (ppm
) of silver (x axis) adsorbed on calcined hydrotalcite (g)
g) is shown. The tested 2 shown in Figure 1a
Of the two systems, 0.25g/containing complexed cyanide and free or background cyanide ions.
I! A solution containing about 0.5 g of total cyanide ions
The amount of silver film deposited on the calcined hydrotalcite adsorbent is greater than the solution containing total cyanide ions of /II. (The pH of the solution obtained after adding the adsorbent was measured to be approximately 10.
It was 5. ) In Figure 1, the adsorption isotherms of calcined hydrotalcite are plotted against the adsorption isotherms of uncalcined hydrotalcite for the removal of silver-cyanide complexes. As is clear from this graph, both adsorbents have p
Excellent effect is shown when H is about 10.5.

In Figure 2, calcined hydrotalcite adsorbent was added in various amounts to a solution containing a gold-cyanide complex. Again, a solution containing 0.25 g/II of the gold-cyanide complex had a greater amount of surface adsorption onto the adsorbent than a solution containing the same complex at a concentration of approximately 0.5 g/1. Ta.

Figure 3 shows the adsorption of silver-thiol by calcined hydrotalcite in solutions with various silver concentrations at a pH of 12:3 and a molar ratio of total thiosulfate ions to silver ions of 10:1. This is a comparison of the amounts of sulfuric acid complexes. Fourth
The figure shows adsorption isotherms of calcined hydrotalcite for solutions containing copper-citrate complexes with varying molar ratios of total citrate ions to copper ions. Figures 5 and 6 show the total E
Copper-EDTA and Nickel-EDTA to Calcined Hydrotalcite at Various Molar Ratios of DTA and Metal Ions
This shows the adsorption amount of the complex. It can be seen from these figures that both calcined and uncalcined hydrotalcite have very good adsorption capacity for metal-ligand complexes, especially at alkaline pH values. At relatively low concentration levels, the ability of calcined hydrotalcite to remove metal complexes or chelates from solution remains very high.

It has been shown that there is some competitive adsorption of free ligand ions on the surface sites of calcined hydrotalcite, although the presence of excess free or uncomplexed ligands reduces the adsorption capacity somewhat. ing.

Although preferred embodiments have been described, it is to be understood that the invention may be practiced otherwise than those embodiments within the scope of the claims.

[Brief explanation of drawings]

Figure 1a is a graph showing the adsorption isotherm of calcined hydrotalcite for a silver-cyanide complex, expressed by the relationship between the silver ion adsorption capacity of the adsorbent and the silver concentration in the solution. Figure 2 is a graph comparing the adsorption isotherms of calcined hydrotalcite and uncalcined hydrotalcite for silver-cyanide complexes; FIG. 3 is a graph showing adsorption isotherms of calcined hydrotalcite for gold-cyanide complexes as a function of concentration; FIG. Figure 4 is a graph showing adsorption isotherms plotting the amount of sulfate complex; Figure 4 shows the adsorption isotherms of calcined hydrotalcite for copper-citrate complexes in solutions with varying molar ratios of total citrate ions to copper ions; FIG. 5 is a graph showing calcined hydrotalcite adsorption isotherms for Cu-EDTA complexes at various values of the molar ratio of total EDTA to copper ions, and FIG. Figure 6 is a graph showing the adsorption isotherms of calcined hydrotalcite for the N1-EDTA complex at various values of the molar ratio of total EDT^ to nickel ions.

Claims (1)

[Claims] 1. (a) The solution has the formula A_wB_x(OH)_yC_z
・nH_2O (wherein A is a divalent metal cation, B is a trivalent metal cation, C is a monovalent to tetravalent anion, w, x
, y, z, and n meet the following conditions: 0≦z≦x≦4≦w
≦1/2y and 12≧n≧3/2x), a calcined product of this compound and a mixture thereof; A method of reducing the amount of anionic metal-ligand complex in a solution, comprising: 2. The compound has the formula A_6B_2(OH)_1_6C.
4. The method of claim 1, comprising 4H_2O. 3. A is selected from the group consisting of Mg^+^2, Ni^+^2, Fe^+^2 and Zn^+^2,
B is selected from the group consisting of Al^+^3, Fe^+^3 and Cr^+^3, and C is OH^-, Cl
^-, Br^-, NO_3^-, CH_3COO^-,
CO_3^-^2, SO_4^-^2, PO_4^-^
3, Fe(CN)_5^-^3 and Fe(CN)_5^
Claim 2 is selected from the group consisting of -^4.
Method described. 4. Claim 1, wherein said compound is selected from natural or synthetic hydrotalcite, pyroolite and tachovite.
Method described. 5. The method of claim 1, wherein said material consists essentially of calcined hydrotalcite. 6. Claim 1, wherein the complex to be removed is divalent or more.
Method described. 7. The metal of the complex is Ag, Au, Ba, Ca, Cd,
Cu, Fe, Mg, Mn, Ni, Pb, Pd, Pt, R
2. The method of claim 1, wherein the metal is selected from a, Rh, Sn, Sr, Ri and Zn. 8. Claim 1, wherein the ligand of the complex is selected from cyanide ion, thiocyanate ion, thiosulfate ion, citrate ion and ethylenediaminetetraacetic acid (EDTA).
Method described. 9. The method according to claim 8, wherein the complex to be removed is a noble metal-cyan complex. 10. The method according to claim 8, wherein the complex to be removed is a silver-thiosulfate complex or a gold-thiosulfate complex. 11. The complexes to be removed are copper-citric acid complex and nickel-
Claim 8 is a citric acid complex or a zinc-citric acid complex.
Method described. 12. The complex to be removed is a metal-EDTA complex, and the metal is Ag, Ca, Cu, Fe, Mg, Ni, and Zn.
9. The method of claim 8, wherein the method is selected from: 13. The method of claim 1, wherein step (a) comprises adding a sufficient amount of the substance to the solution to remove substantially all of the complex. 14. The method of claim 1, wherein step (a) comprises passing the solution through a container whose contents consist essentially of the substance. 15. The method of claim 1, wherein step (b) comprises removing the substance from the solution by one or more of filtration, gravity sedimentation, and centrifugation. 16. A method of treating a solution containing an environmentally unacceptable amount of an anionic metal-ligand complex, the method comprising: (a) formula A_6B_2(OH)_1_6C·4H_2O;
(In the formula, A is Mg^+^2, Ni^+^2, Fe^+^
2 and Zn^+^2, and B is selected from the group consisting of Al^+^3, Fe^+^3 and Cu^+^3
selected from the group consisting of, C is OH^-,
Cl^-, Br^-, NO_3^-, CH_3COO^
-, CO_3^-^2, SO_4^-^2, PO_4^
-^3, Fe(CN)_5^-^3 and Fe(CN)_
(b) contacting the solution with an amount of said compound sufficient to reduce its complex content to less than about 1 ppm; The above method comprising the steps of: 17. Prior to the step (b), about 400°C to 650°C
17. The method of claim 16, further comprising calcining the compound at one or more temperatures between. 18. Step of removing complex saturated compounds from the solution (c
17. The method of claim 16, further comprising: ). 19. The metal of the complex is Ag, Au, Ba, Ca, Cd
, Cu, Fe, Mg, Mn, Ni, Pb, Pd, Pt,
17. The ligand is selected from Ra, Rh, Sn, Sr, V and Zn, and the ligand is selected from cyanide ion, thiocyanate ion, thiosulfate ion, citrate ion and ethylenediaminetetraacetic acid (EDTA). the method of. 20. The method according to claim 19, wherein the complex is a noble metal-cyanide complex or a noble metal-thiosulfate complex. 21. The method of claim 19, wherein the complex is a metal-EDTA complex and the metal is selected from Ag, Ca, Cu, Fe, Mg, Ni and Zn. 22. The method of claim 16, wherein step (b) comprises contacting the solution with an amount of the compound sufficient to reduce its complex content to less than about 0.1 ppm. 23. A solution containing a metal-cyanate complex, a metal-thiocyanate complex or a metal-thiosulfate complex is treated with a sufficient amount of a compound consisting essentially of a compound selected from hydrotalcite, calcined hydrotalcite and mixtures thereof. 1. A method for substantially all removal of a metal-cyanate, metal-thiocyanate or metal-thiosulfate complex from a solution containing the complex, the method comprising contacting the metal-cyanate, metal-thiocyanate or metal-thiosulfate complex with an amount of the substance. 24, comprising contacting a solution containing a metal-citric acid complex with a sufficient amount of a substance consisting essentially of a compound selected from hydrotalcite, calcined hydrotalcite, and mixtures thereof. A method for removing substantially all of a metal-citric acid complex from a solution containing the complex. 25. Contacting a solution containing a metal-ethylenediaminetetraacetic acid (EDTA) complex with a sufficient amount of a substance consisting essentially of a compound selected from hydrotalcite, calcined hydrotalcite, and mixtures thereof. metal-ethylenediaminetetraacetic acid (EDTA), including
A method for removing substantially the entire amount of a complex from a solution containing the complex.