AU767164B2 - Method of magnesium production - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

S.

Name of Applicant: Actual Inventors: Address for Service: Invention Title: Russian National Aluminum and Magnesium Institute Alumw* A 9 'iesr &vrtroees L\i^\W Josif L. Reznikov and Vladimir I. Schegolev and Ludmi Abramova BALDWIN SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 'METHOD OF MAGNESIUM PRODUCTION' 0: 0 6

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5* F E, S The following statement is a full description of this invention, including the best method of performing it known to me/us:- File: 26871AUP00 1A METHOD OF MAGNESIUM PRODUCTION Field of the Invention This invention relates to the electrolytic methods of magnesium production. The method of magnesium production is applicable to metallurgical and chemical processing of sea water, brine of salt lakes, natural carnallite and other *mineral salts of magnesium, as well as carbonates and other oxide compounds of magnesium both mined in the natural conditions and waste products from mining operations and 10 other mineral processing.

Background of the Invention The method of magnesium production from sea water and oyster shells consisting of pure CaCO 3 is known in the prior art. The shells are burned and then slaked with water. A lime milk solution produced during the slaking of shells is used to precipitate magnesium hydroxide from sea water. The precipitated magnesium hydroxide is then neutralized with hydrochloric acid. This acid is a byproduct of chlorine gas production at the anodes of the electrolytic cells and thereafter of the reduction of the same to hydrogen chloride. The hydrogen chloride is then reacted with water to form the acid. The magnesium chloride-containing solution that was formed is evaporated, pretreated to remove impurities, dehydrated and then brought to a molten condition. In the process, the slime containing magnesium oxide is separated and clarified and thereafter is subjected to electrolysis. The produced anodic gas is -2transformed into hydrochloric acid which is recirculated to initial phase of the process (See, M.A. Eydenzon "Magnesium", Metallurgy, pages 115-124 [Moscow, 1969]; and German Patent No. 1,082,740 dated November 24, 1960).

The drawbacks of this and other similar prior art methods of production of molten magnesium chlorides are as follows: agglomeration of the bischofite MgC12-6H20 (produced during the drying of the liquor) and substantial hydrolysis of the bischofite.

This results in a requirement for technologically sophisticated equipment with high construction costs. Such operations are often harmful to the environment. All the above mentioned factors considerably reduce the viability of producing dehydrated magnesium chloride by the dehydration of its crystalline hydrates (see M.A. Eydezon, supra; at p.

121). It should be noted however, that since the 1980's "Norsk Hydro" company utilizes this technology at its plants. (See S.L. Stefaniuk "Metallurgy of magnesium and other light metals", Metallurgy, p. 28-29 [Moscow; 1985]).

More recently, there is increasing popularity of methods of producing magnesium from various initial raw materials in which there is the intermediate formation of artificial carnallite (MgC12KCI-6H 2 It is known that the dehydration of carnallite is much easier than that of bischofite MgC1 2 6H 2 0.

There is a known method of producing magnesium from a chlorine-magnesium liquor which is a by-product of the production of potassium sulfate from naturally 20 occurring chloride-sulfate salts of potassium-magnesium. The magnesium production is accompanied by the formation of an intermediate product, artificial camallite. (see O.A.

Levedev "Production of magnesium by electolysis", Metallurgy, p. 33-34 [Moscow; 1988]).

^1 C C sC 0 C C C C C C C CC CC CC C C C C C CC C CC C C C C CC C C C CCC C CC CC CC CC C CC C CC C CC According to this method, a slurry of the spent electrolyte or molten salt bath and slurry of potassium chloride are added to the purified chlorine-magnesium liquor and six-water carnallite results therefrom. After the crystallization, the carnallite is separated from the mother liquor by precipitation and centrifugation. The mother liquor is then returned back to the initial phase of the process. Initial dehydration of the solid carnallite occurs in the fluidized bed dryer. The balance of the dehydration process occurs in the melt in the chlorinators.

Chlorine, produced during the electrolysis of carnallite melt, is used in part during the final dehydration of carnallite in the melt in the chlorinators and in other production areas. The spent electrolyte or 15 molten salt bath is recirculated to the raw material inflow for the formation of artificial carnallite.

The above-described method is applicable to a specified composition of initial raw material (potassium-magnesium ores containing sulfur and chlorine compounds) and is also applicable to the production facilities for treatment of the .raw material accompanied by production of magnesium and other chemical substances.

This method has some considerable disadvantages. One e of drawbacks is the increased consumption of chlorides, especially potassium chloride. The increased consumption of chlorides is the result of their losses at the mineral-salt production and is also the result of substantial mechanical losses of chlorides because of the discharge along with slime from the chlorinators and electrolytic cells.

Furthermore, as part of the liquor should be evacuated to avoid accumulation of harmful impurities in the system, (for example boron), there are substantial mechanical losses of the chlorides with the circulating chlorine-magnesium liquor.

In addition, the increased consumption of potassium chloride is also caused by incomplete conversion of potassium chloride and bischofite (MgCl 2 "6H 2 0) into carnallite. As a result, in order to reduce the hydrolysis and to decrease the number of closing of the fluidized bed dryers due to fusion of bischofite, the molar ratio KCl:MgC1 2 is maintained substantially equal to 1.11. This factor also increases the losses of potassium chloride in all production areas.

Another drawback of the above discussed method is in the use of the artificial carnallite having a high content of sodium chloride, i.e. content in the range of 7.5 to 12% S 15 (See Russian Federation Patent No. 1,736,094 dated December 1993). Such level of sodium chloride is related in parts to its presence in the utilized secondary liquors of magnesium chloride. Such level of sodium chloride results in the decreased capacity of the fluidized bed dryer and in 20 the increase of fuel consumption. The latter increase is *due to the need to reduce the temperature of the heat transfer medium in the dryer. The reduction of the heat transfer medium latter is explained by the formation of S" fusible compounds containing NaC1 which might lead to highly undesirable burning off the dryer.

The above discussed ratio of KCl:NaCl 2 and the NaCl content are recommended in the prior art literature. In this respect, see the above-mentioned leaflet USSR, Moscow, and Russian Federation Patent No. 1,736,094 dated October 12, 1993, where in Table 4 in the "Recommended Examples of the Method", the content of sodium chloride in carnallite is shown to be between 12.1 and 8.8 percent.

The above drawbacks are critical not only for the above described prior art method, but also critical for the electrolytic production of magnesium using artificial carnallite produced from sea water and other natural materials. This is especially true for those materials containing magnesium in the form of its oxygen compounds which are pretreated with hydrochloric acid prior to inclusion in the magnesium chloride liquor.

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

Summary of the Invention According to a first aspect, the invention provides a method of producing magnesium from an artificial carnallite formed by the pre-treatment of magnesiumbearing raw materials and waste waters to provide a magnesium chloride solution which in turn is combined with potassium chloride, sodium chloride, a first recirculated aqueous effluent and a second recirculated aqueous effluent, said first recirculated aqueous effluent being formed after pre-treatment from precipitates are separated therefrom by centrifugation thereof, said method of producing magnesium including the ••steps of dehydrating the precipitants with a heat transfer medium produced by burning •fuel in a primary air supply; subsequent cooling of the combustion products with 20 secondary air; electrolytically producing magnesium, chlorine gas and said second recirculated aqueous effluent, and comprising the following additional steps: supplying said chlorine gas into a hot flame from the combustion of a hydrogen bearing fuel for the complete or partial reduction thereof to hydrogen chloride gas; dehydrating the artificial carnallite in a heat transfer medium of a fluidized bed, said fluidized bed having additional thermal energy supplied thereto from heating devices therewithin; cooling of the overheated heat transfer medium with secondary air; absorbing the hydrogen chloride gas from the exhaust gases of the dehydration process into the aqueous solution circulating in the gas scrubber to produce hydrochloric acid of a predetermined concentration; a .a .a a. •a a o. ooo ao. a ao• a a. a. a pretreating separately or together a slurry of oxygen compounds of calcium and/or magnesium with said hydrochloric acid to produce calcium chloride and/or magnesium chloride; and, alternatively directly absorbing said hydrogen chloride gas from the exhaust gases of the dehydration process into said slurry to produce calcium chloride and/or magnesium chloride.

According to a second aspect, the invention provides a method of producing magnesium from an artificial carnallite formed by the pre-treatment of magnesiumbearing raw materials and waste waters to provide a magnesium chloride solution which in turn is combined with potassium chloride, sodium chloride, a first recirculated aqueous effluent and a second recirculated aqueous effluent, said first recirculated aqueous effluent being separated after pre-treatment from precipitates settling therefrom and being separated by centrifugation thereof, said method of producing magnesium including the steps of dehydrating the precipitants with a heat transfer medium produced by burning fuel in a primary air supply; subsequent cooling of the combustion products with secondary air, electrolytically producing magnesium, chlorine gas and said second recirculated aqueous effluent, and comprising the following additional steps: maintaining the molar ratio of potassium chloride to magnesium chloride in the artificial carnallite preparation for dehydration in the range between 0.9 and 1.05.

•00 20 According to a third aspect, the invention provides magnesium produced by a method according to the first aspect.

~According to a fourth aspect, the invention provides magnesium produced by a S" method according to the second aspect.

This invention relates to a method of magnesium production which includes the preparation of carnallite from a magnesium chloride solution in combination with potassium and sodium chlorides. The mother liquor is separated from a solid phase by settling and/or centrifugation. Thereafter, the remaining liquid phase is returned to the beginning of the process. After the step of separation, the solid phase is dehydrated by heated gases produced by the combustion of fuel in the primary air supply.

Subsequently, the combustion products are cooled by a secondary air supply. Processing in the gas scrubbers and the electrolytic action of the continuous processing line produces magnesium chlorine and spent electrolyte. Optionally, the spent electrolyte is partly or completely returned to the process. Initially, chlorine released during the electrolytic action, is partially or completely reduced to hydrogen chloride. To do this, the chlorine is fed into a high-temperature, hydrogen-bearing flame. Thermal energy for dehydrating the artificial carnallite is derived from two sources. First, during the process, the heat transfer medium becomes overheated and creates residual thermal energy in the fluidized bed. As the heat transfer medium cools, the artificial carnallite is dehydrated by this residual thermal energy. Secondly, any additional thermal energy required for the dehydration of the artificial carnallite is supplied through heating devices located within the fluidized bed and the contacting of the :artificial carnallite thereby. During processing hydrochloric acid of a predetermined concentration is formed S 15 in the gas scrubber upon the recirculation of the aqueous solution thereof absorbing the previously described hydrogen chloride. This hydrochloric acid is, in turn, used to pretreat any oxygen compounds of calcium and magnesium present in the initial raw material or intermediates used in the production of magnesium chloride solution. The .resultant solutions are used during the production of artificial carnallite so as to generate calcium and magnesium chloride solutions. In the operation, all initial S" components are introduced into the artificial carnallite production process to assure the following content of the components in the artificial carnallite, in the percent by weight proportions (in wt. potassium chloride 21.0 25.0; magnesium chloride 30.0 32.0; sodium chloride 3.5 calcium chloride 0.3 water remaining Additionally, molar ratio of calcium chloride with respect to magnesium chloride is maintained within the range 0.9 1.05.

The solid phase, produced during the production of artificial carnallite is washed with the solution of calcium chloride.

As described above, the neutralization of hydrogen chloride by the aqueous solutions of oxygen compounds of calcium such as lime milk, for example, produces calcium 10 chloride. The solution formed thereby is recirculated to the artificial carnallite preparation stage. This step facilitates removal of sulfate impurities from the magnesium .chloride liquor. The calcium chloride solution is also .utilizable for cleaning of artificial carnallite from mother liquor containing magnesium chloride and used for impregnation of the artificial carnallite.

***The solid deeply-dehydrated, low-hydrolyzed carnallite produced during the step of dehydration in the stream of heated gases containing hydrogen chloride is fed into the 20 melt for the electrolytic production of magnesium, chlorine and spent electrolyte.

Upon accumulation of calcium chloride in the cycle, 0e S"sodium sulfate or magnesium sulfates are introduced into the magnesium-chloride solution before the production of artificial carnallite. The resultant solid calcium sulfate precipitates out of solution.

It is known that increasing the sodium chloride content of the electrolyte increases the conductivity thereof and reduces respectively the electric energy consumption of the electrolytic process. Thus, when there is insufficient content of sodium chloride in the initially supplied raw material, it is added directly to the melt of the electrolytic process.

The above discussed specific features of the invention contribute to the reduced consumption of potassium chloride in the formation and treatment of artificial carnallite and decrease consumption of electrical energy in the magnesium production. Furthermore, the invention increases the yield of magnesium from carnallite and the capacity of fluidized bed dryers utilized in the carnallite dehydration. In the fluidized bed dryers, besides the increased capacity, the reduction of energy consumption occurs because processing proceeds at higher temperatures of the heat transfer medium used in the fluidized bed. Still further, the invention results in a decrease of labor costs for dryer maintenance.

gO .15 This is because the number of closings of the dryers by fusion of bischofite and the interruptions incurred thereby for the required cleaning are substantially reduced.

In addition, the method of the invention is usable with sea water as the initial raw material for the magnesium 20 production. With sea water, the initial phase involves precipitation of magnesium hydroxide which is then further processed. The invention also provides direct utilization of oxygen compounds of magnesium. The sea water and oxygen compounds reaction with hydrogen chloride gas and 25 hydrochloric acid results in the production of chlorinee. :magnesium-containing solution.

The reduction in the consumption of salts, particularly potassium chloride, occurs because of the greater efficiency in the processing cycle compared to the prior art. The improved efficiency results from: reduced hydrolysis which results from a decrease in the quantity of free magnesium chloride present in the artificial carnallite during the washing thereof prior to the dehydration step; -9and, by dehydration of the artificial carnallite in the stream of heated gases containing hydrogen chloride. These conditions reduce the hydrolysis and provide deeply-dehydrated, low-hydrolyzed carnallite which is supplied directly into the electrolytic cells. Thus, a final stage of dehydration in the chlorinators is eliminated.

The invention enables the avoidance of considerable losses of chlorides, which are typically discharged with slime from the chlorinators. Furthermore, the invention considerably reduces the specific consumption of electrical energy during the production of magnesium. This is because thermal energy losses from the surface of the chlorinators and from the exhaust gases discharged from these devices are minimized.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

Description of the Preferred Embodiments 15 In the method of the invention which follows, the production of magnesium from an artificial carnallite is described. An artificial camrnallite is formed by pretreating magnesium-bearing raw materials and waste waters. For the purposes of this disclosure, artificial carnallite is defined as the product formed by mixing potassium chloride and magnesium chloride solutions in substantially equal molar proportions, the combined solutions thereof further including limited amounts of calcium chloride and sodium chloride therein and being suitable for dehydration and subsequent electrolytic processing to produce magnesium and chlorine. The pretreatment of the raw materials is S. completed by centrifugation and, after separating the precipitant therefrom, the remaining first aqueous effluent is recirculated so as to combine either partially or fully with the pretreated raw material. Similarly, the electrolytic phase of the process produces magnesium, chlorine, and a second aqueous effluent or spent electrolyte, which effluent is also recirculated so as to combine either partially or fully with the pretreated raw materials. In the invention, the recirculation of the spent electrolyte reduces the specific consumption of potassium chlorides without the risk of excessive accumulation of calcium chloride in the cycle.

However, if and when the accumulation of calcium chloride occurs, such accumulation is controlled by precipitating calcium sulfate from the magnesium chloride solution upon sodium or magnesium sulfates being introduced thereinto.

The above-mentioned reduction of potassium chloride consumption is especially important when such component is .:0 15 absent or is present in small quantities within the initial raw material. The reduction of potassium chloride consumption is also important for the above described technology of producing chlorine-magnesium solutions from sea water.

o 20 The reduction of the specific consumption of potassium chloride is further achieved by reducing the molar ratios of potassium chloride to magnesium chloride from 1.05 1.11 to *o o0.9 1.05 in the cycle. This occurs without increasing the hydrolysis of carnallite and without closings of the dryers 25 by fusion of bischofite. The bischofite is crystallized upon drying of the mother liquor containing more than 20% of magnesium chloride, and impregnating carnallite. As discussed hereinabove, this takes place as a result of washing the artificial carnallite with calcium chloride 30 solution in the centrifuge. Accordingly, 80% of mother liquor is substituted with the calcium chloride solution.

As the calcium chloride is not subjected to the agglomeration, this avoids the closing of the dryers by fusion and the increase of the temperature of the thermal transfer medium supplied into the bed. This results in the increase of the capacity of the dryers and the decrease in the consumption of the electrical energy and of labor costs for maintaining the dryer.

Similar results are obtained by reducing the lower limit of sodium chloride content in the artificial carnallite. This increases the temperature of the heated gases under the grid of the last chamber of the dryer without the risk of the formation of fusible elements closing the grid. The consumption of electrical energy during the electrolysis is not increased, as upon demand, additional sodium chloride is fed into the molten carnallite or directly into the electrolytic cells.

In the process of this invention, the calcium chloride for removing sulfur-containing compounds from the chlorinemagnesium liquor and for the washing of artificial carnallite is provided as a by-product of the gas cleaning system. Here, upon the absorption of hydrogen chloride with by lime milk, calcium chloride is produced.

Table 1 provides four sets of performance characteristics: one for the prior art performance and four other examples for the performance under the method of the invention. The Examples i, 2 and 3 relate to the processing 25 of the secondary processing stage of the magnesium chloride solution, produced upon the calcium chloride treatment of natural potassium-magnesium chlorides-sulfates salts hereinbefore described. The Example 4 relates to utilization of a solution of magnesium chloride produced from sea water as the initial raw material. Also, in Table i, the performance parameters of the prior art device adopted arei the known optimal results for the operation for .the modernized fluidized bed dryer. [Table 1 is attached.] 12 It follows from Table 1 that the method of the invention reduces the specific consumption of potassium chloride by 17.5 to 35 percent and increases the thermal efficiency of the fluidized bed dryer for the dehydration by as much as 9.3 percent and as little as 8.1 percent. The process further enhances the thermal efficiency by increasing the average heating gas temperatures from 3800 C to the range of 430' to 4400 C, whereas the specific consumption of the fuel and electrical energy is reduced in the range of 8.5 to 7.5 percent. The productivity of the fluidized bed dryer is similarly increased.

The specific consumption of electrical energy for the operation of the electrolytic cell is reduced by 2.4 to KWH/t of Mg, and the magnesium extraction from the 15artificial carnallite is increased on 7 to 9 percent.

The above-discussed figures do not reflect the increase of performance and the reduction of the labor costs resulting from the reduced number of the furnace cleanings and do not reflect the additional savings in consumption of 20 electrical energy resulting from operating the electrolytic cells at a greater current efficiency.

The invention shows that operating at a molar ratio of KCI:MgCl 2 below 0.9 is inadvisable. This is because, as mentioned hereinabove, during the single washing of crystals 25 in the centrifuge by calcium chloride liquor, about percent of the excessive magnesium chloride is substituted by calcium chloride. To remove the remainder of free magnesium chloride, it is necessary to wash crystals once again with calcium chloride. This results is an undesirable 30 quantity of calcium chloride being accumulated and recirculated in the process. The increase of the ratio KCI:MgC1 2 over 1.05 is similarly undesirable.

Reducing the lower limit of sodium chloride content in the artificial carnallite enables the invention to increase the temperature of the heated gases during dehydration.

This consequently reduces the consumption of the fuel and electrical energy and increases the fluidized bed dryer capacity. Upon introducing the fluidized bed dryer output into the electrolytic cell, if the electrical conductivity of the electrolyte in the cells is insufficient, additional sodium chloride is provided so as to adjust the electrical conductivity of the cell. When the content of sodium chloride is low in the initial raw material, the additional quantities of sodium chloride are added at the later stages of the carnallite production or directly into the bath of the electrolytic cells.

e:oo The method of the invention is carried out as follows.

carnallite is produced from an aqueous solution of magnesium chloride, potassium chloride, sodium chloride and calcium chloride. If the primary raw material is sea water, the first step of the method is precipitation of magnesium hydroxide with lime milk. The magnesium hydroxide is treated with hydrochloric acid to produce a chlorinemagnesium containing solution. The acid is produced as a by-product of treating the gaseous effluent from the dehydration stage of the process, and specifically from the 25 effluent containing hydrogen chloride gas which is formed upon the reduction of chlorine at the anode of the electrolytic cell. The reduction reaction occurs when chlorine is in the presence of the combustion of hydrogenbearing fuel. Also, under the electrolytic cell conditions, some hydrogen chloride gas is formed by direct production of hydrogen-chloride from chlorine and hydrogen. The dehydration of carnallite in the stream of gases containing hydrogen chloride reduces the hydrolysis and enables the process to go forward at a ratio of KCI:MgCl 2 lower than the corresponding prior art ratio.

When oxygen compounds of magnesium are used as raw material, the process is similar to the above. Chlorides of potassium, sodium and calcium are mainly supplied to the process by returning spent electrolyte from the electrolytic cells. Such supply is in the form of a slurry with water or in the form of a slurry with mother liquor, and any additional potassium chloride required is supplied by the same route.

The losses of the salt components and of chlorine in the cycle are compensated by adding dried or dehydrated o .o carnallite. With the addition of dried carnallite, the point of addition is at the initial stage of dehydration, which stage is completed in the solid condition. With the addition of dehydrated carnallite, the point of addition is at the final stage of the process.

i By using various additives at suitable points of addition, potassium, sodium, calcium and magnesium chlorides content is regulated. Magnesium chloride content is 25 regulated by the addition of an aqueous solution MgC1 2 or by addition of bischofite.

If desired, a portion of the calcium chloride required for pretreating or cleaning the chlorine-magnesiumcontaining solution and for washing the artificial 30 carnallite (see below) is produced by neutralization of hydrogen chloride gas with lime milk. The neutralization occurs in the gas scrubber and the recirculated aqueous solution therefrom is used for pretreatment.

When the brine of chlorine-magnesium-containing lakes or secondary chlorine-magnesium liquors are used as initial raw material, the process begins directly by evaporating and pretreating these liquors, mainly to remove the sulfates.

This is accomplished by using calcium chloride or barium chloride to avoid magnesium hydroxide formation.

After the production of artificial carnallite, crystallization, precipitation and centrifugation, the crystals of carnallite impregnated with mother liquor the chlorine-magnesium-containing solution are produced. To minimize the quantity of the impregnating solution, the crystals are washed in the centrifuge with a calcium chloride solution.

S..All initial components are introduced into the process in the ratio that provides the following content by weight of the components of the artificial carnallite as prepared 20 for dehydration: Component by wt. range Min. Max.

potassium chloride 21.0 25.0 25 magnesium chloride 30.0 32.0 S* sodium chloride 3.5 calcium chloride 0.3 water the rest The molar ratio of potassium chloride to the magnesium chloride is maintained at substantially equal proportions between 0.9 and 1.05.

0* 9

S

9 9 0 *9 09 9 9* 0* 16 If after the washing of the artificial carnallite, the calcium chloride content in the carnallite exceeds the permissible value of approximately 2% by weight, sodium sulfate or magnesium sulfate is introduced into the chlorine-magnesium-containing solution before production of the artificial carnallite. Furthermore to remove the excess calciuim, the solid calcium sulfate CaS04 is precipitated.

Two examples of the method of the invention, applied to two types of the initial raw material are presented in Table 1. One of the examples utilizes the step of washing the carnallite to increase the quality thereof. However, for better comparison the examples are presented reflecting identical quantities of the initial chlorine-magnesium liquor and also showing practically the same content of magnesium chloride and potassium chloride in the solution.

The numbers of the examples correspond to the numbers in Table 1 (initial raw material chlorine-magnesium liquQr, produced as waste runoff at a treatment site of fossilized salts).

Example 1 (Table 1) 1449.2 tons of chlorine-magnesium liquor is produced from waste runoff at a treatment site of fossilized chlorides-sulfates and has the sulfates removed therefrom by a known method. This aqueous solution contains (in wt. MgC1 2 26.03; KC1, 2.0; NaC1, 0.91; CaC1 2 0.5; CaSO 4 0.8; and water 69.76. This liquor is mixed with the recirculating -mother liquor, containing (in MgC1 2 22.9; KC1, 1.33; NaC1, 1.33; CaC12, 1;86; CaSo 4 0.11; and water 72.47. Then, a portion of 'the water is evaporated from the mixture of liquors. Then, 245 tons of spent "electrolyte in the form of a slurry and 33 tons of :i r commercial potassium chloride are introduced into the evaporated liquor. The content of spent electrolyte is as follows KC1, 77.14; NaC1, 15.3; MgC1 2 5.4; CaC1 2 2.16. The content of commercial potassium chloride is as follows KC1, 95.0; and, NaC1, 5.0. To prepare the slurry, 100 t of water is used. The mixtures are agitated for 40 minutes to produce an artificial carnallite. After the production thereof, the mixture is sent to the vacuum crystallization unit to produce the suspension of carnallite. This process is accompanied by the additional evaporation of water. After the steps of settling and centrifuging, 1000 tons of artificial carnallite is obtained containing (in wt. MgC1 2 31.6 KC1, 24.5; NaC1, 4.8 CaC12, 0.65 CaSO 4 0.05 and H 2 0, 38.4 as well as the **Po 15 clarified mother liquor of the above mentioned composition.

The major portion of this liquor is returned to the beginning of the process and 325 tons of the mother liquor is removed from the process to avoid the accumulation of harmful boron compounds and other impurities. During the 20 process 502.2 tons of water are evaporated. The balance of the carnallite production is given in the attached Table 2.

The artificial carnallite undergoes dehydration in the *0 continuous fluidized bed dryer. In the dryer, the first stage of the dehydration of carnallite occurs by removing up 25 to the content of 3 moles of water per mole of magnesium chloride.

The second stage or final part of the dehydration takes place in a batch process mode by introducing into the combustion chamber of a furnace the following components: hydrogen-bearing fuel, air necessary for the combustion thereof, and anodic chlorine gas in quantity of 0.9 ton per ton of produced electrolytic magnesium. Upon the introduction of the chlorine gas into the high temperature flame of the combusted fuel, the chlorine gas is reduced into the hydrogen chloride gas. The flue gases, exhausted from the combustion chamber and containing hydrogen chloride are dissolved by the secondary air and sent for the final dehydration into the fluidized bed. The optimal temperature range of the fluidized bed is found to be 300° to 3500 C. The gases and particulates exhausted from the fluidized bed are separated from each other. The separated particulates are returned to the fluidized bed and absorbed by sprayed lime milk in the wet gas scrubber. The calcium chloride solution produced in the gas scrubbing system is recirculated. During the dehydration process, the irretrievable losses reach up to 1.5 percent of the supplied artificial carnallite. Furthermore, 2 percent of such carnallite is hydrolyzed in the fluidized bed, forming magnesium oxide and hydrogen chloride.

As a result of the dehydration of 1000 tons artificial carnallite, 600.9 tons of solid deeply-dehydrated lowhydrolyzed carnallite are unloaded from the fluidized bed.

This carnallite contains (in wt. %):MgCl 2 50.44; KC1, 39.94; NaCI, 7.62; CaCl 2 1.05; CaSO 4 0.08; H 2 0, 0.44; and, MgO, 0.44. This output from the fluidized bed is loaded into electrolytic cells. During loading about 2 percent of each component and 4 percent of sodium chloride is lost or evacuated along with gases drawn therefrom. Furthermore, because of the remaining water and moisture in the air drawn into the cell, 1 percent of MgCl 2 is hydrolyzed in the melt.

Thus, per 1000 tons of artificial carnallite delivered to the cells, (600.9 X 0.5044) (0.98 0.01) 294.00 tons of ,0 magnesium chloride is obtained.

According to the published data, obtained from Metallurgical practice, (see, M.A. Eydenzon, supra, at p.

321, table 581), 93.87 percent i.e. 276 tons of the'

I/

magnesium chloride is subjected to the electrolysis and the rest remains in the spent electrolyte or is evacuated along with the slime and fumes.

Theoretically as a result of the electrolysis 70.36 tons of Mg (magnesium) and 205.8 tons Cl (chlorine) should be produced. This means that 2.92 tons of Cl should be produced per one ton of magnesium. However, in practice, when the method of the invention is utilized, 2.7 tons of Cl per one ton of magnesium is produced. The remainder is mainly evacuated with exhaust gases flowing from the cathode aspiration. Of this amount, 0.9 tons of chlorine per ton of magnesium is recirculated to the fluidized bed dryer and :.126.7 tons are used as a commercial product.

Thus, the rate of extraction of magnesium from 15 artificial carnallite is about 87.3 percent and the rate of extraction of commercial chlorine from carnallite is about 62.2 percent. Additionally, 290.8 tons of spent electrolyte is obtained having the following composition (wt. KC1, 77.14; NaCI, 15.3; MgCl 2 5.4; and, CaCl 2 2.16. From this amount, 245 tons of spent electrolyte is recirculated for o the production of artificial carnallite and the .remainder is used for by-products such as flux,i fertilizer or roadway fill material.-- 25 Example 4 (Table 1) The initial raw material is a solution of magnesium chloride produced from sea water by a known method.

1449.2 tons of the solution has sulfates removed therefrom by a known:,:method. The solution is formed by treating the .magnesium hydroxide with -hydrochloric acid.! The magnesium hydroxide is produced by :precipitation from sea water by reaction of the magnesium chloride contained in the sea water with lime milk. The conten of the lime milk is as follows: (wt. MgC1 2 25.97; KC1, 2.0; NaC1, 1.60; CaCl2, 0.5; CaSO 4 0.06; H 2 0, 69.87. The pretreated initial raw material is mixed with the recirculating mother liquor containing in combination MgCl1, 21.86; KC1, 1.31; NaC1, 1.31; CaC12, 5.06; CaSO 4 0.11; and H 2 0 70.35. Then a part of water is evaporated from the mixture of liquors and 245.45 ton of slurry of spent electrolyte is introduced.

The content of spent electrolyte is as follows (wt. MgCl 2 5.37; KC1, 66.66; NaC1, 22.02; and, CaCl2, 5.96.

Furthermore, 26.0 tons of commercial potassium chloride, containing KC1, 95.0; and, NaCl, 5.0 is introduced thereinto. To prepare slurries, 100 tons of water is used.

To produce artificial carnallite the mixture is agitated for 15 40 min. Then, the mixture is fed to the vacuum crystallization unit to produce a suspension of carnallite.

During this process, additional water evaporated.

After settling, the condensed suspension is fed into the centrifuge where the clarified mother liquor is separated. The main part of the clarified mother liquor is provided for further processing thereof to the inlet of the fluidized bed dryer. To avoid the accumulation of harmful boron compounds and other impurities 324.9 tons of S: the clarified mother liquor is removed from the process.

25 During the process 495.75 tons of water is evaporated from the liquors. A 1000 t quantity of artificial carnallite impregnated with mother liquor remains in the centrifuge.

This carnallite contains (wt. MgCl 2 31.85; KC1, 21.30; NaC1, 7.43; CaC 2 0.54; CaSO 4 0.65; and, H 2 0, 38.23.

During the evacuation of the mother liquor, the artificial carnallite is washed in the centrifuge with a calcium chloride solution. For this purpose 100 tons of 23 21 percent of calcium chloride solution is utilized. At this technological step, 80 tons of mother liquor are substituted in carnallite by 80 tons of the calcium chloride solution.

The composition of washed carnallite in quantity of 1000 tons is as follows: (wt. MgCI 2 30.1; KCl, 21.2; NaCl, 7.3; CaC1 2 1.96; CaSO 4 0.04; and water, 39.4.

Simultaneously therewith 100 t of flushing water is evacuated from the centrifuge and removed from the process, as containing the increased quantity of boron. The composition of this water includes MgCl 2 17.49; KCI, 1.05; NaCl, 1.05; CaC1 2 8.65; CaSO 4 0.088; and H 2 0, the rest.

Table 3 provides further details of production and washing of the carnallite preparation and washing.

15 The washed artificial carnallite is then introduced into the continuous fluidized bed dryer for the initial dehydration stage. There the dehydration is continued until the water content reaches 2 moles of water per one mole of magnesium chloride. As distinct from Example i, in the present instance, the furnace is heated by a high o temperature flame created by the combustion of a hydrogen bearing fuel in air and the furnace is supplied with 0.9 t of anodic chlorine gas per ton of produced electrolytic magnesium. In this process, the chlorine gas is reduced to hydrogen chloride gas. The heated gases released from the combustion chamber of the furnace are diluted by a secondary air to the extent necessary to adjust the processing temperature. These heated gases are provided to the fluidized bed wherein the temperature range is maintained between 1750 and 140 0 C.

The second and final part of the dehydration occurs as a batch process. The remaining anodic chlorine (about 1.8 tons of chlorine per ton of electrolytic magnesium produced) is supplied to the previously described high-temperature flame of a hydrogen containing fuel. The process continues until the bed temperature is between 3000 and 35 0 0 C.

The particulate matter and the gases exhausted from the fluidized bed dryer are separated and the particulates recovered are returned to the dryer. Then, a gas scrubber absorbs the hydrogen chloride gas forming hydrochloric acid.

In this step, the system is sprinkled with slurry of magnesium hydroxide and water produced from sea water.

Alternatively, circulating water is used to absorb the hydrogen chloride gas. Either absorption step is accompanied by the formation of hydrochloric acid which, in turn, is utilized for the production of a chlorinemagnesium-containing solution from the solution containing 15 magnesium-hydroxide.

Similar to the Example 1, the irretrievable losses of salt components during the dehydration process can reach up to 1.5 percent of the supplied artificial carnallite.

Furthermore, compare to Example i, due to the high concentration of hydrogen chloride in the gases, in the present instance, 1 percent, (compared to 2 percent in Example 1) of magnesium chloride is hydrolyzed in the fluidized bed. The quantity of remaining water is reduced respectively.

25 The dehydration of 1000 t of artificial carnallite (of above mentioned composition) is accompanied by unloading from the fluidized bed of 593.2 t of solid deeply-dehydrated low-hydrolysed carnallite. This carnallite contains (wt. MgCI 2 49.38; KCI, 35.03; NaCl, 11.77; CaCI 2 3.20; CaSO 4 0.067; H 2 0, 0.33; and, MgO, 0.21.

This product is supplied into the electrolytic cell.

Two percent of each component and 4 percent of sodium chloride are lost irretrievably because of evacuation thereof with effluent gases. Furthermore, about 0.5 percent of MgCI 2 is hydrolyzed in the melt as a result of the remaining water and moisture in the ambient air.

Thus, per 100 tons of washed artificial carnallite, the melt contains 593.2 -0.4938 (0.98 0.5) 285.6 tons of MgCI 2 As discussed hereinabove with reference to Example 1, only 93.87 percent of magnesium chloride are subjected to the electrolysis. The remainder is contained in the spent electrolyte and is evacuated together with slime and fumes.

As a result of the electrolysis, although theoretically, 68.41 tons of magnesium and 149.9 tons of :.:":chlorine should be produced. However, in practice, 2.7 tons of chlorine per ton of magnesium is manufactured. Thus, according to the method of the invention, 184.7 tons of chlorine is generated and sent into the fluidized bed dryer.

The extraction of magnesium from artificial carnallite is about 89.07 percent. In addition, 287.1 tons of spent electrolyte is obtained. The composition of the spent electrolyte is as follows (wt. MgC 2 5.37; KCI 66.66; NaCl, 22.02; and, CaC1 2 5.96. Of this amount, 245.45 tons is recirculated for the production of artificial carnallite and the remainder is used for by-products such as flux, fertilizer, or roadway fill material.

While the above description has provided information about the method of this invention, the production of magnesium from an artificial carnallite is facilitated by certain inventive steps, which steps are presented below, but not in any sequential order. The specific steps are as follows: -24supplying said chlorine gas into a hot flame from the combustion of a hydrogen bearing fuel for the complete or partial reduction thereof to hydrogen chloride gas; dehydrating the artificial carnallite in a heat transfer medium of a fluidised bed, the fluidised bed having additional thermal energy supplied thereto from heating devices therewithin; cooling of the overheated heat transfer medium with secondary air; absorbing the hydrogen chloride gas from the exhaust gases of the dehydration process into the aqueous solution circulating in the exhaust gas scrubber to produce hydrochloric acid of a predetermined concentration; pretreating separately or together a slurry of oxygen compounds of calcium and/or magnesium with said hydrochloric acid to produce calcium chloride and/or magnesium chloride; alternatively directly absorbing the hydrogen chloride gas from the exhaust gases of the dehydration process into the slurry to produce calcium chloride and/or magnesium chloride; washing the precipitate produced during artificial carnallite preparation with a solution of calcium chloride; upon the neutralization if the hydrogen chloride gas from the exhaust 20 gases of the dehydration process with oxygen compounds of calcium (lime milk), °•separating the calcium chloride solution produced thereby and the recirculation thereof to the initial stage of the artificial carnallite preparation to clean the liquor of magnesium chloride of sulfates and/or the artificial carnallite of magnesium chloride bearing mother liquor which impregnates the camallite; 0• 0 000 0 o 00 0 00 00 00 00 00 0 00 0 0 0 0 0* feeding into the melt in the cells of a continuous production line the solid deeply-dehydrated, low-hydrolyzed carnallite produced upon dehydration of artificial carnallite for the electrolytic production of magnesium, chlorine and spent electrolyte; upon accumulation of calcium chloride within in the cycle, introducing sodium and magnesium sulfates into the liquor of magnesium chloride before the synthesis, and precipitating the solid calcium sulfate produced from the liquor; adjusting the sodium chloride concentration in the raw material for electrolysis to increase the conductivity of the electrolyte and reduce respectively the power consumption for the electrolysis, the sodium chloride being 15 directly added to the melt subjected to electrolysis; maintaining the molar ratio of potassium chloride to magnesium chloride in the artificial carnallite Spreparation for dehydration in the range between 0.9 and 1.05; maintaining the potassium chloride component of the materials introduced into the process in the 21.0 to -25.0 per cent by weight range; maintaining the magnesium chloride component of the materials introduced into the process in the 30.0 to 1 25 32.0 percent by weight range.

[o0] maintaining the sodium chloride component of the materials introduced into the process in the 3.5 to percent by weight range; and, maintaining the calcium chloride component of the materials introduced into the process in the 0.3 to percent by weight range.

While the invention has been taught with specific i reference to the above-described embodiments, those skilled 26 in the art will recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. Thus, the described embodiments are to be considered in all respects only as illustrative and not restrictive.

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S. S S *5 Table 1 CHARACTERISTICS AND PERFORMANCES OF THE PROCESS No Name and unit of measurement 1 Carnallite composition, wt.% KC1 MgCl 2 NaCl CaC12 CaSO4

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2 0 Prior Examples of the method Art of the invention 1 2 3 4 25.0 30.0 7.45 0.5 0.05 37.0 24.5 31.6 4.8 0.65 0.05 38.4 23.5 30.9 6.0 0.95 0.05 38.6 22.3 30.3 7.0 1.36 0.04 39.0 21.2 30.1 7.3 1.96 0.04 39.4 2 Ratio KC1: MgCl 2 fraction of mole 1.05 3 Consumption of potassium chloride(95%) 40.0 (ton per 1000 ton of artificial carnallite) 4 Thermal efficiency of the fluidized 59 bed dryer for dehydration of carnallite in the solid condition, Reduction of the specific consumption 0 of fuel, electric energy and increase of the FB dryer capacity by increasing the thermal efficiency, 6 Number of the FB dryer cleanings 4 per month 7 Reduction of the specific consumption 0 of electric energy, (thousand kWt./ h per 1 ton 0.99 0.97 0.94 0.90 33.0 31.0 28.0 26.0 64.5 64.3 64.1 63.8 8.5 8.2 7.9 3 2 1.5 8 Extraction of magnesium from carnallite (81.4-82.3) 87.3 89.1 *Estimated values (see I.L. Reznikov, G.Y. Sandler Non-ferrous metals, 1987, No7, p. 67.) **Estimated values (see I.L. Reznikov, G.Y. Sandler Non-ferrous metals, 1980, No. 10, p. 93.) Tabl e 2 BALANCR OF THE CAUOXALLITE PRODUCTION (Example 1) Namue Quantity, Components NaCl 13.19 MgClz CaClz SUPPly CaSO 4 0.87 Initial desuiphat ed liquor Spent electrolyte 1449.2 28.98 377.20 7.25 1021.7 245.0 188.99 37.48 13.23 5.29 Potassium 33.0 chloride Water for 100.0 the suspension formation TOTAL 1827.2 31.35 1 100.0 249.32 52.32 390 43 10 KA A 0'7 3QflA~4 1) ~A a., I qq,%4 Consumption Artificial carnallite Excessive mother liquor Evaporated. water 1000.0 245.0 48.0 4.32 316.0 74.43 325.0 502.2 4.32 0.50 0.37 6.04 384.0 235.5 502.2

TOTAL

iOA 827.2 249 -4 2 .U.3 12.54 0.87 1121.7 BALANCE OF THE CARNALLITE PRODUCTION AND WASHING (Evxaple 4) Name Quantity, Components Table 3 Page 1 C aSO (ton) KCl NaCi MgC12 Production, Supply CaC12 Ini tial desuiphated liquor Spent electrolyte Potassium Chloride 1449.2 28.28 23.18 376.31 7.24 0.87 1012.62 245.45 163.62 5A.04 13.17 14.62 26.00 24.70 1.36 Water for 10o.0o the suspension formation TOTAL 1820.65 100.0 217.30 78.52 389 48 11 cc A a-? 7852 AR n n 217.30 Production, consimiption Artificial carnallite (non-washed) Excessive mother liquor Evaporated water 1000.0 213.05 74.27 318.47 71.01 5.43 16.43 0.50 388.28 0.37 228.59 324.9 495.75 4.25 4.25 495.75 TOTAL 1820.65 217.30 78.52 389.48 21.86 0.87 112.67 .v 1 Washing, su;p1V Artif icial carnallite (non-washed) 1000.0 213.05 74.27 318.47 5.43 0.50 388.28 Potassium chloride liquor

TOTAL

100.0 23.00 77.00 7A -37 1100.00 213O 05' -a-a 1 a- 43 0.5 46.2 Washing, consumption Washed artificial carnallite Flushing water from centrifuge

TOTAL

1000.0 212.00 73.22 300.98 19.64 Table 3 Page 2 0.412 393.74 0.088 71.54 100.0 1.05 1 .05 17.49 8.79 1100.0 213.05 7d ~7 A 4 V z 652 Sumarized process, supply Initial desuiphated liquc 1449.2 28.28 23A18 376.31 7.24 13.17 14.62 0.870 1012.62 Spent electrolyte Potassium chloride Potassium chloride liquor 245.45 163.62 54.04 26.00 100.00 160.00 24.70 1.30 23.00 77.00 100.00 water for formation of the suspension TOTAL 1920.65 217.30 78.52 389 AR AA CC I~ L.L Oar 0 A .&ZUQ 10rCHMALMA cons 4-4 0 ~Ma.~U DrDcinun.

Artificial carnallite (washed) 1000.0 212.00 73.22 300.98 19.64 0.412 393.74 0.370 228.59 Excessive mother liquor Flushing water from centrifuge Evaporated water 324.9 100.0 495.75 4.25 1.05 4.25 1.05 71.01 16.43 17.49 8.79 0.088 71.54 495.75

TOTAL

1920 65 111 2n -P TOA Q2~ 112~ a a.9 .30V 4 44.86 0.870 1189.62

Claims (13)

1. A method of producing magnesium from an artificial carnallite formed by the pre- treatment of magnesium-bearing raw materials and waste waters to provide a magnesium chloride solution which in turn is combined with potassium chloride, sodium chloride, a first recirculated aqueous effluent and a second recirculated aqueous effluent, said first recirculated aqueous effluent being formed after pre-treatment from precipitates are separated therefrom by centrifugation thereof, said method of producing magnesium including the steps of dehydrating the precipitants with a heat transfer medium produced by burning fuel in a primary air supply; subsequent cooling of the combustion products with secondary air; electrolytically producing magnesium, chlorine gas and said second recirculated aqueous effluent, and comprising the following additional steps: supplying said chlorine gas into a hot flame from the combustion of a hydrogen bearing fuel for the complete or partial reduction thereof to hydrogen chloride gas; dehydrating the artificial carnallite in a heat transfer medium of a fluidized bed, said fluidized bed having additional thermal energy supplied thereto from heating devices therewithin; cooling of the overheated heat transfer medium with secondary air; absorbing the hydrogen chloride gas from the exhaust gases of the dehydration process into the aqueous solution circulating in the gas scrubber to produce hydrochloric acid of a predetermined concentration; pretreating separately or together a slurry of oxygen compounds of calcium and/or magnesium with said hydrochloric acid to produce calcium chloride and/or 25 magnesium chloride; and, alternatively directly absorbing said hydrogen chloride gas from the exhaust gases of the dehydration process into said slurry to produce calcium chloride and/or magnesium chloride. oo

2. The method of claim 1 further comprising the step of washing the precipitate produced during artificial carnallite preparation with a solution of calcium chloride.

3. The method of claim 1 or claim 2, further comprising the steps of producing a calcium chloride solution upon the neutralization of hydrogen chloride solution gas from the exhaust gases of the dehydration process with oxygen compounds of calcium (lime 0 0 0: o •e -32- milk) and recirculating said calcium chloride solution to the artificial carnallite preparation stage for cleaning the liquor of magnesium chloride of sulfates and/or the artificial carnallite of magnesium-chloride-bearing mother liquor which impregnates the carnallite.

4. The method of any one of claims 1 to 3, comprising the step of: feeding the solid deeply-dehydrated, low-hydrolyzed carnallite, produced upon dehydration of artificial carnallite in the stream of heated gases containing hydrogen chloride, into the melt of electrolytic cells within a continuous production line for producing magnesium, chlorine and spent electrolyte.

5. The method of any one of claims 1 to 4, comprising the following additional steps: upon accumulation of calcium chloride within the cycle, introducing sodium sulfate .and/or magnesium sulfate into the liquor of magnesium chloride before the preparation of artificial carnallite, calcium sulfate produced from the liquor. S6. The method of any one of claims 1 to 5, further comprising the step of adjusting oo.o.i the sodium chloride concentration in the initial raw material for increasing the conductivity of the electrolyte and reducing respectively the power consumption for the electrolysis, said sodium chloride being directly added to the melt subjected to electrolysis.

S.i

7. The method of any one of claims 1 to 6 further comprising the step of maintaining the molar ratio of potassium chloride to magnesium chloride in the artificial carnallite preparation for dehydration in the range between 0.9 and 1.05.

8. A method of producing magnesium from an artificial carnallite formed by the pre- :treatment of magnesium-bearing raw materials and waste waters to provide a magnesium chloride solution which in turn is combined with potassium chloride, sodium chloride, a first recirculated aqueous effluent and a second recirculated aqueous effluent, said first recirculated aqueous effluent being separated after pre-treatment from precipitates settling therefrom and being separated by centrifugation thereof, said method of producing magnesium including the steps of dehydrating the precipitants with a heat transfer medium produced by burning fuel in a primary air supply; subsequent cooling of the combustion products with secondary air, electrolytically producing magnesium, chlorine gas and said second recirculated aqueous effluent, and comprising the following additional steps: -33 maintaining the molar ratio of potassium chloride to magnesium chloride in the artificial carnallite preparation for dehydration in the range between 0.9 and 1.05.

9. The method of claim 8 further comprising the steps of: a) maintaining the potassium chloride component of the materials introduced into the process in the 21.0 to 25.0 per cent by mass range; and, b) maintaining the magnesium chloride component of the materials introduced into the process in the 30.0 to 32.0 percent by mass range.

The method of claim 9 further comprising the steps of: c) maintaining the sodium chloride component of the materials introduced into the process in the 3.5 to 9.5 percent by mass range; and d) maintaining the calcium chloride component of the materials introduced into the process in the 0.3 to 2.0 percent by mass range.

11. Magnesium produced by a method according to any one of claims 1 to 7.

12. Magnesium produced by a method according to any one of claims 8 to

13. A method of producing magnesium from artificial carnallite substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying examples but excluding comparative examples. S DATED this 20th day of May 2002 RUSSIAN NATIONAL ALUMINIUM AND MAGNESIUM INSTITUTE (VAMI) Attorney: PAUL G. HARRISON Fellow Institute of Patent and Trade Mark Attorneys of Australia of BALDWIN SHELSTON WATERS