Cominco, Ltd.

Comino Ltd.

Daniel A Boateng

Donald L Ball

Godefridus M Swinkels

Cashman R Hampton

David A Neudorf

Victor N Saleh

Victor E Steiner

A process is provided for the removal of fluoride from a metal sulphate solution, such as a zinc sulphate solution, which presents an option for the disposal of waste treatment sludge from the aluminum anodizing industry. The fluoride is removed from metal sulphate solution by mixing the sludge with the solution for a predetermined period of time and then performing a solid/liquid separation.

Fluoride removal from metal sulphate solution and a method of waste

Cyanide-containing solution is subjected to two-stage membrane electrolysis in units each comprising a cathode, an anode and one or more bipolar electrodes interspaced with cationic membranes defining alternating anode and cathode compartments containing anolyte and catholyte, respectively. Electrolysis causes generation of hydrogen cyanide in the recirculating first stage anolyte, and alkali metal hydroxide is formed in the recirculating first-stage catholyte. The hydrogen cyanide is stripped from the first stage anolyte and is subsequently absorbed in catholyte in an absorption unit for the recovery of alkali metal cyanide-containing solution. Partially cyanide-depleted first-stage anolyte is mixed with an amount of an alkali metal chloride and passed as second-stage anolyte through the second-stage unit for the generation of chlorine with destruction of residual cyanide in the anolyte and the formation of alkali metal hydroxide in the recirculating second-stage catholyte from which a portion is directed to the absorption. A substantially cyanide-free effluent is withdrawn from the circulating second-stage anolyte. To allow for the formation of solid precipitates in the anolyte of the membrane electrolysis stages, the width of the anode compartments may be increased to at least 5 mm. Electrolysis is carried out at current densities in the range of 20 A/m.sup. 2 to 350 A/m.sup.2 and at ambient temperatures.

Method for the recovery of cyanide from solutions

Zinc is selectively extracted from zinc sulfate solutions that may also contain sulfuric acid and amounts of other metals with an organic extractant mixture containing both organic substituted phosphoric acid and organic substituted thiophosphinic acid. The phosphoric acids are preferably chosen from mono- and di-2-ethylhexylphosphoric acids and mixtures thereof, and the phosphinic acids are preferably chosen from bis- 2, 4, 4-trimethylpentyl mono- and dithiophosphinic acids. The use of an extractant mixture of the dithiophosphinic acid with mono- and di-2-ethylhexyl phosphoric acids or an extractant mixture of the dithiophosphinic acid with di-2-ethylhexylphosphoric acid is preferred. The pH during zinc extraction is controlled at a value in the range of about 1.3 to 5. Control of pH is carried out either by neutralization or by acid extraction with an organic amine-type extractant. The acid content of the feed solution may be reduced by neutralization or acid removal by dialysis. The solvent extraction of zinc or zinc and acid from feed solution may be carried out co-, counter- or cross-currently in one or more stages. The preferred extraction method is dualcircuit, side-by-side, simultaneous zinc and acid extraction. The use of the mixed extractant for zinc is more effective than extraction with the component extractants by themselves.

Method for the solvent extraction of zinc

Electrodialysis is used to separate at least one species of a first group of elements present in ionized form from at least one species of a second group of elements present in nonionized form in water-containing solutions, provided that the pH of the solutions and the oxidation state of species of the second group have the appropriate values. If necessary, either the pH, the oxidation state or both are adjusted in the solution fed to the electrodialysis unit such that species of the first group are present in ionized form and species of the second group are present in a nonionized form. The method is applicable to a large number of solutions from metallurgical and chemical processes. Species of the first group include at least one element of groups IA, except Fr, IB, IIA, IIB, IIIA except B, IIIB, IVB, VIIB and VIII except Os of the periodic table; the elements V, Cr, Sn, Pb and Bi; and acids of N, S, F, Cl, Br and I. Species of the second group comprise acids containing at least one element including B, C, Si, Ge, P, As, Sb, Se, Te and F. Electrodialysis is carried out in one of more stages at 10-500 A/m.sup.2 and 0.degree.-60.degree. C. while minimizing water splitting, and using alternating cationic and anionic permselective membranes forming alternating concentrate and diluate cells between an anode and a cathode. The ionized species migrate through the membranes from the diluate to the concentrate cells and the nonionized species remain in the diluate cells. Solution concentrated in ionic species is withdrawn from the concentrate cells, and solution containing the nonionized species is withdrawn from the diluate cells. The electrode compartments are rinsed with appropriate rinse solutions.

Method for separating dissolved species by electrodialysis

There is provided a method for treating zinc-containing sulfate solutions which comprises an acid removal for the recovery of a substantially pure sulfuric acid solution and a solution low in acid and containing the zinc and metal impurities from the sulfate solution. The acid removal is carried out by a membrane process that consists of dialysis, electrodialysis or dialysis integrated with electrodialysis. The dialyzate or diluate is subjected to a dual-circuit, side-by-side, simultaneous solvent extraction of zinc and sulfuric acid. In one circuit sulfuric acid is extracted from the dialyzate or diluate and the raffinate from the zinc extraction with an amine-containing extractant. Acid is stripped from the loaded organic with water or an alkaline substance, and is recovered as sulfuric acid or as a sulfate, preferably as ammonium sulfate. In the other circuit, zinc is extracted from the raffinate from the acid extraction with an organic phosphoric-, phosphinic-, phosphonic- or thiophosphinic acid-containing extractant. The zinc is stripped from the loaded organic with acid, and is recovered as a concentrated zinc sulfate solution. A residual solution substantially containing the impurities is removed from the process. The extraction and stripping may be carried out in one or more stages.

Method for treating zinc-containing sulfate solution

Insoluble mercury salts and any mercury in mercury-containing material are converted into a soluble form by controlled chlorination. The soluble forms of mercury in the chlorination solution are reduced with iron, preferably iron powder, to elemental mercury. After separation from the reduced solution, the solids from the reduction containing entrained mercury, are subjected to a separation for the separation and substantially quantitative recovery of substantially pure mercury. Separation by elutriation through a body of mercury is preferred. Prior to separation, the reduction solids may be kneaded for coalescence of fine mercury particles, followed by slurrying of the kneaded material. Any selenium in the reduced solution may be recovered in a reduction with a suitable reductant, preferably by adding strong sulfuric acid in the presence of the ferrous chloride formed in the preceding reduction, and excess sulfur dioxide. The process is carried out at ambient conditions, and the amount of liquid in the process is controlled. Substantially no mercury is discharged from the process in residues, or residual liquid.

Method for the recovery of mercury from mercury-containing material

An arsenate solution is treated by electrolysis with membranes for at least partial conversion into arsenic acid and hydroxide. Electrolysis is carried out in an electrolytic unit containing an arrangement of electrodes and membranes. Depending on the electrode and membrane type and configuration, arsenic acid having a reduced content of alkali metal or ammonium cations and impurities is recovered. Arsenic acid-containing solution and hydroxide solution are removed. An electrolysis unit comprises, preferably, a stack of 2- or 3-compartment cells, comprising at least one electrode/membrane group arranged between terminal electrodes with or without terminal membranes. Each group may comprise a bipolar or a monopolar electrode in combination with either cationic or cationic and anionic membranes. Hydroxide and acid compartments are defined between electrodes and membranes, and diluate compartments may be defined between membranes.

Method for making arsenic acid

In a process for the manufacture of copper arsenate, an arsenic-containing material is subjected to an oxidative pressure leach with sodium hydroxide forming a leach solution containing sodium arsenate. Sodium arsenate solution is mixed with a solution of copper sulfate for the formation of a copper and arsenic-containing solution without the precipitation of copper arsenate. The copper and arsenic-containing solution is treated for the precipitation of copper arsenate with formation of sodium sulfate solution. At least one of the sodium arsenate-containing solution and the sodium sulfate solution is subjected to electrolysis with membrances for at least partial conversion to arsenic acid and sulfuric acid, respectively, and sodium hydroxide. The generated sodium hydroxide is used in the process, the sulfuric acid may be a by-product or is recycled for use in the preparation of copper sulfate solution, and the arsenic acid is used instead of sodium arsenate in the formation of the copper and arsenic-containing solution.

Process for the manufacture of copper arsenate

An improved method for selectively rcovering Ge from acidic solution containing Ge and typically Zn, As, Cd, Sb, In, Cu and Fe (II) by multistage, countercurrent liquid-liquid extraction is described. The extractant used in the organic phase is an oxime, for example, 5,8-diethyl-7-hydroxy-6-dodecanone oxime, mixed with at least one alkylphosphoric acid, for example either di-2-ethylhexyl phosphate alone or admixed with mono-2-ethylhexyl phosphate, dissolved in a hydrocarbon diluent. This mixed system shows better efficiency and selectivity for germanium than known systems using either oximes or alkylphosphoric acids separately.

Recovery of germanium from aqueous solutions by solvent extraction

Monovalent ions, especially chloride and fluoride, but also thallium, sodium and potassium are efficiently removed from ZnSO.sub.4 electrolyte by electrodialysis. Monovalent anions are removed using alternating monovalent anion permselective membranes and cation exchange membranes. Monovalent anions and cations are removed using alternating monovalent anion and monovalent cation permselective membranes. Electrodialysis is carried out under turbulent conditions, at up to 60.degree. C., a differential membrane pressure of less than 150 kPa, a current density of 10 to 500 A/m.sup.2, and a pH of less than 5.5. Where both chloride and fluoride are removed a pH of 3.5 to 5.5 is maintained. Deposition of manganese and zinc on the electrodes is minimized by at least one of a number of means including arranging the membranes such that the end membranes are monovalent anion permselective; selecting a large electrode rinse flow; adding a small amount of soluble antimony and/or cobalt; and using a cathode made of a material that promotes hydrogen evolution over zinc deposition. The electrode compartments are preferably rinsed with a 0.1 to 1.0 M Na.sub.2 SO.sub.4 solution at pH 0 to 4.

Method for removal of monovalent ions from ZnSO.sub.4 electrolyte by

Lithium-containing brines containing mono and multivalent cations, especially magnesium, and anions are treated by electrodialysis to effect separation of a lithium concentrate low in multivalent cations from which lithium can be recovered as chloride, sulfate, or carbonate. Brine containing 0.03 to 15 g/L Li and a ratio of Mg:Li as high as 60:1 is subjected to one or more electrodialysis steps. The preferred cationic and anionic membranes are those that are strongly acidic and have sulphonic acid radical and trimethylamine derivatives, respectively, as active groups at 3 to 4 milligram equivalent per gram of dry resin and have a matrix of styrene divinyl benzene copolymer on a pvc base. Electrodialysis is carried out at a pH below 7 under turbulent conditions. The number of electrodialysis steps depends on the permselectivity of the membranes, the Mg:Li ratio in the feed and that in the concentrate, the latter being maintained at 5:1 or less. The chloride concentration in the electrode compartments is maintained at less than 3 g/L. In multi-step electrodialysis, a portion of the magnesium may be removed in an intermediate stage by the addition of lime, the lithium in the resulting solution being further concentrated by electrodialysis.

Method for the recovery of lithium from solutions by electrodialysis

Germanium is recovered from aqueous solutions containing germanium, zinc, and antimony by sorption with an ion exchange resin which has as its matrix a backbone polymer to which are attached amine active groups chosen from secondary and tertiary amines and quaternary ammonium groups. The resin exhibits a high selectivity ratio of germanium relative to antimony. The method is particularly useful for the recovery of germanium from materials or electrolytes encountered in the recovery of zinc from ores and complex concentrates.

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Montrose, Canada

Daniel A Boateng