WO1991008318A1

WO1991008318A1 - Metal oxide production by leaching and hydrolysis

Info

Publication number: WO1991008318A1
Application number: PCT/AU1990/000568
Authority: WO
Inventors: David Royston
Original assignee: Mineral Process Technology Pty Ltd
Priority date: 1989-12-01
Filing date: 1990-11-27
Publication date: 1991-06-13

Abstract

The invention is directed to the processing of mineral ores, particularly to the production of metal oxides from metal sulphides, especially antimony sulphides. The process is of the type whereby the ore is first leached by a suitable lixiviant and the thus-leached material is susbsequently subjected to hydrolysis, the improvement comprising first separating the leached material from the lixiviant before the hydrolysis is undertaken. This separation is preferably achieved by crystallization. This improved process requires the use of less noxious and relatively inexpensive reagents, reaction conditions are less extreme, it is possible to recycle a significant quantity of reagents/solvents, a more reactive intermediate product is achieved, the final product is of a high quality and the secondary products are also of commercial value.

Description

METAL OXIDE PRODUCTION BY LEACHING AND HYDROLYSIS

TECHNICAL FIELD

THIS INVENTION relates to the processing of mineral ores. More specifically, it is directed to the production of metal oxides from metal sulphides. The present invention is particularly suitable for the production of antimony oxide from antimony sulphide bearing minerals.

BACKGROUND ART A number of processes have been proposed for the production of antimony oxides from antimony sulphide concentrates.

For example, the conventional pyrometallurgical method for the production of antimony oxide is to roast stibnite concentrates in air which results in the sublimation of the volatile antimony oxide product.

Disadvantages of this method include: the co- volatilisation and entrainment of impurities such as arsenic oxide, lead and iron compounds, trace sulphides and sulphur dioxide; the requirement to treat further the impure oxide to produce a high quality product; and the production of sulphur dioxide which has to be treated by absorption or other means to avoid atmospheric pollution.

Alternative hydrometallurgical processes have also been proposed such as that described in US Patent 2,331,395 which refers to the "Sunshine Process" wherein antimony metal is recovered electrolytically from an antimony leach liquor produced by the selective sodium sulphide leach of antimony-bearing sulphide concentrates. Similar electrolytic processes have also been described in the USSR and in China.

However, such electrolytic processes are limited to production of a metal which needs to be processed further to form an oxide.^' In addition, further process steps are necessary to recover the sulphur component of the original feed materials. For example, in the electrolytic processes referred to above, sodium sulphide is usually recovered by crystallization and then recycled to the leach liquor.

Alternative prior art processes also include the selective leach of stibnite from a concentrate using ammonium sulphide, followed by recovery of the sulphide by distillation of the leach liquor (as described in US Patent 3,883,635). The recovered sulphide is then converted to the oxide and sulphur by digestion in nitric acid. Difficulties arise in the practical handling of malodorous ammonium sulphide as well as the limited commercial value of the elemental sulphur by- product.

In US Patent 3,944,653, chlorination of stibnite concentrates is described giving antimony trichloride and sulphur or hydrogen sulphide as by-products. The antimony chloride (purified by distillation) is hydrolised to antimony oxide. However, the initial chlorination step cannot be expected to be selective for antimony and thus purification of the intermediate antimony trichloride is required. In addition, chlorination generally results in sulphur production as a low value by-product..

In French Patent 7,608,963, antimony concentrates are converted to chlorides by attack with calcium chloride, SO- and oxygen. The product chloride is purified by distillation and then hydrolised to the oxide. Sulphur is discharged ultimately as a sulphate waste. Yet another process uses gaseous attack of hydrogen chloride on stibnite concentrates to produce an antimony chloride intermediate. After its purification by distillation, the antimony chloride is converted to the oxide by hydrolysis. Sulphur in the concentrate is converted to hydrogen sulphide and, in turn, to sodium sulphide. The overall cost of such a process may be commercially prohibitive.

In addition to the above processes, a number of others have been suggested for the conversion of antimony trichloride into antimony oxide. For example, US Patent 3,917,793 describes the production of a light-stable εenarmontite by hydrolysis of antimony trichloride below 40°C and at a pH from 7 to 10. The earlier reference to US Patent 3,883,635 describes a final thermal treatment step involving heating the oxide to 500°C.

All of these prior art processes generally suffer from one or more disadvantages, including difficulties in handling noxious reagents or by-products, extreme reaction conditions necessary to produce the final, high quality product and/or the co-production of by-products of limited commercial value. Further, with regard to those prior art processes utilising acid hydrolysis, this, acidification also destroys any remaining lixiviant necessitating its re-generation from the hydrolysis by¬ products before re-cycling as leach liquor. This adds to the complexity and cost of these processes. DISCLOSURE OF THE INVENTION

It is a general object of the present invention to overcome, or at least ameliorate, one or more of the above problems and to provide a process for the production of a high purity metal oxide which maximises the useful life of the reagents utilised in the process.

In particular, it has been established that by first separating the metal-bearing material from the leach liquor before subjecting that material to further processing, (1) significant quantities of unspent lixiviant can be recovered and immediately recycled as leach liquor with its original leaching capacity substantially maintained and (2) the thus-separated metal-bearing material is significantly more reactive towards subsequent processing.

According to the present invention, there is provided a process for the production of an oxide of metal from a metal-bearing material said process being of the type whereby said metal-bearing material is first leached by a suitable lixiviant and the thus-leached material is subsequently subjected to hydrolysis, wherein said thus- leached material is first separated from said lixiviant before said hydrolysis is undertaken.

Preferably, said leached material is separated from said lixiviant by crystallization.

Preferably, said metal-bearing material is leached in a solution of a sulphide salt. More preferably, said sulphide salt is either sodium sulphide or a sulphide of said metal. Most preferably, said sulphide salt is a sodium said metal sulphide salt. Preferably, said sodium said metal sulphide salt crystal obtained after separation is converted to a chloride of said metal before being subjected to hydrolysis.

The reaction conditions required for this invention obviously may vary with the nature and quantity of reactants used. Generally, however, it has been found that the present invention is particularly suited to the preparation of high purity antimony trioxide from antimony sulphide-containing ores.

Preferably, an aqueous, sodium antimony sulphide leach liquor is used to leach antimony sulphide from its concentrates, this leach liquor being initially prepared by the addition of sodium sulphide liquor to the antimony sulphide concentrates. The leach liquor is readily filtered. The gangue produced can be processed by conventional means to recover any precious metal content. A quantity of sodium antimony sulphide solid is crystallized from the leach liquor, the balance of sodium antimony sulphide remaining in solution being utilised again as a component of the recirculating leach liquor after compensating for the sodium sulphide extracted (with the antimony) from the leach liquor into this solid by the addition of sodium sulphide to the recirculating leach liquor to restore its original composition as it is returned to the leach stage.

The sodium antimony sulphide solid is converted into antimony trichloride, sodium sulphate and hydrogen sulphide by reaction with acids. Sufficient concentrated sulphuric acid is added to convert the sodium into sodium sulphate and sufficient approximately azeotropic hydrochloric acid is also added to convert the antimony into antimony trichloride. (Those skilled in the art will appreciate that a mixture of common salt and sulphuric acid could be used to generate hydrochloric acid in situ. ) The hydrogen sulphide liberated in the reaction can be absorbed subsequently, for example, in sodium hydroxide. The sodium sulphate is recovered after the acidification step from the resulting liquor.

The antimony trichloride solution is heated under reflux and aerated to eliminate soluble sulphide then hydrolised with water sufficient to form antimony

^"pentoxydichloride, Sb.Clj-O-, and hydrochloric acid for recycling after concentration by evaporation.

The antimony pentoxydichloride is converted into antimony trioxide by hydrolysis, preferably by reaction with a base such as ammonia, sodium hydroxide or sodium carbonate under alkaline conditions.

DETAILED DESCRIPTION OF EMBODIMENTS

Specific details of the reagents and the reactions involved in the process stages of this invention are illustrated in the following example. In this example, all temperatures are in degrees Centigrade, and technical terms have the usual meaning in the art. Crude reaction products can be purified by the means described herein, or by other means known in the art.

EXAMPLE

Initial Preparation of the Leach Liquor

530 g of (65% Sb) antimony sulphide concentrate was added to a solution of 444 g of technical grade (60% Na_S) sodium sulphide liquor in 1100 ml of distilled water heated to 80°. This pulp was mixed vigorously and kept within 80 to 95°C for 30 minutes. Sodium antimony sulphide solids were crystallized from the leachate. The solids were then filtered free of liquor.

Subsequent Preparation of the Leach Liquor

The leachate from above after separation of the solids was adjusted in sodium sulphide concentration by the addition of 47g of technical grade sodium sulphide (60% Na₂S) and heated to 80°C whereupon 137g of 65% antimony in sulphide concentrate were added and mixed vigorously until fully dissolved. The pulp from the leach was filtered as described above to provide a residue and a leach liquor.

Recovery of Sodium Antimony Sulphide

The leach liquor was concentrated to induce the crystalization of sodium antimony sulphide solids with an approximate composition _. aSbS₂ of a mass approximately equivalent to the Na₂S and Sb₂S₃ contents of the rea _*gents added to the leach.

Conversion to antimony trichloride

The sodium antimony sulphide solids were heated under reflux with 0.3 Molar sulphuric acid and 6 Molar hydrochloric acid. The liquor was filtered from a minor amount of residue.

Formation of oxychloride

Liquor containing antimony trichloride and hydrochloric acid was hydrolised by adding distilled water to produce a white fine crystalline precipitate of antimony pentoxydichloride, Sb₄0--Cl₂. This was filtered clear of leach, liquor.

Oxychloride to oxide

White antimony trioxide produced by the ambient temperature sodium carbonate solution reaction with the oxychloride contained very low levels of arsenic, lead, iron and sulphur as contaminants.

By using the present invention, metal-bearing, particularly antimony-bearing, concentrates are converted into a high purity metal oxide. Additional valuable products which may be obtained include sulphides, hydrosulphides and sulphates.

In an initial recovery and purification stage, the process uses selective leaching of metal-bearing material followed by its recovery from solution which is carried out' in normal materials of construction associated with hot alkaline solutions, thus avoiding the need for high duty materials necessary for high temperature prior art chloride systems. This step also provides both the lixivation and purification stage of the process without the need for additional purification usually necessary following broad spectrum dissolution with chlorination or hydrochloric acid attack.

The present invention is particularly suited for the leaching of metal sulphide-bearing material whereby, after the above-described recovery and purification stage, the metal sulphide is converted to a metal chloride in a reaction.with low tenor hydrochloric acid. The hydrogen sulphide liberated is recovered by absorption in, for example, sodium hydroxide which can be further processed to products for both recycle and sale.

In a further stage, the metal chloride liquor is hydrolysed under controlled conditions to form a metal oxychloride. This procedure permits a large part of the hydrochloric ^' acid produced in the reaction to be recycled (after concentration) for use in the earlier stage.

In the final stage, metal oxide is produced by the hydrolysis of the metal oxychloride under alkaline conditions.

It will be appreciated from the above that the present invention provides a number of advantages over the prior art including (1) the use of less noxious and relatively inexpensive reagents, (2) reaction conditions which are less extreme, (3) a recycling of a significant quantity of reagents/solvents and a more reactive intermediate product requiring less reagent for the next stage in the process, both factors contributing to the lower overall cost of the process, (4) the obtaining of a high quality final product, and (5) the obtaining of secondary products which are also of commercial value.

Of course, it will be recognised that the above examples are given by way of exemplification of the invention only, and that changes may be made to the details set out therein without departing from the scope of the invention as defined in the following claims.

Claims

1. A process for the production of an oxide of metal from a metal-bearing material said process being of the type whereby said metal-bearing material is first leached by any suitable lixiviant and the thus-leached material is subsequently subjected to hydrolysis, wherein said leached material is first separated from said lixiviant before said hydrolysis is undertaken.

2. A process as defined in Claim 1, wherein said leached material is separated from said lixiviant by crystallization.

3. A process as defined in Claim 1 or Claim 2, wherein said metal-bearing material is a metal sulphide- bearing material.

4. A process as defined in Claim 3, wherein said metal sulphide-bearing material is leached in a solution of a sulphide salt.

5. A process as defined in Claim 4, wherein said sulphide salt is a sulphide of said metal.

6. A process as defined in Claim 5, wherein said sulphide of said metal is a sodium said metal sulphide.

7. A process as defined in Claim 6, wherein said sodium said metal sulphide is prepared from the reaction between said metal sulphide-bearing material and sodium sulphide.

8. A process as defined in any one of Claims 4 to 6, wherein any balance of said sulphide salt remaining in solution after said leached material is first separated is recirculated as a component of said lixiviant.

9. A process as defined in any one of Claims 1 to 8 wherein said leached material after separation is converted to a chloride of said metal before said hydrolysis is undertaken.

10. A process as defined in Claim 9, wherein said chloride of said metal is hydrolysed to an oxide of said metal.

11. A process as defined in any one of Claims 1 to 10, wherein said metal-bearing material is an antimony- containing ore.

12. A process as defined in Claim 11, wherein said ore is an antimony sulphide-containing ore.

13. An oxide of metal whenever prepared by a process as defined in any one of Claims 1 to 12.

14. A process as defined in Claim 1 substantially as described with reference to the Example.

15. An oxide of metal substantially as described with reference to the Example.