FI63598C - SULFATERINGSFOERFARANDE - Google Patents

Description

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Canada (CA) 1U6U20 (71) The International Nickel Company of Canada, Limited, Copper Cliff,

Ontario, Canada (CA) (72) Christopher Charles Dunkley, Sudhury, Ontario, Canada (CA). This invention relates to the sulfation of metals, and more particularly to the treatment of process residues containing non-ferrous metals, by sulphation to recover non-ferrous metals and any precious metals. (7M 0y Kolster Ah (5I +) Sulfation method - Sulfateringsförfarande.

Precious metal-containing residues, such as anode sludge containing metals in metallic, sulfide and / or oxidized form f, are conventionally slurried with concentrated sulfuric acid and heated in furnaces or other equipment to temperatures of 150 to 500 ° C to sulfate any parent metals present. The residue is then extracted with water to recover sulfated parent metals and to enrich the extract residue with precious metals, which residue can be treated in known ways to recover the precious metals.

Conventional sulfation methods have had to be performed on a small scale and usually in batches, due to structural problems normally associated with the design of a continuous process. Sludge-type sulfation processes are usually used on a small scale, mainly due to externally heated vessels, which have material selection problems and cause heat exchange problems when using acid-resistant materials that do not provide efficient heat exchange. High-efficiency immersion heating or heating by immersion combustion methods are practical, but of low efficiency or cause problems as a droplet with large amounts of exhaust gas. Neither method is suitable for heat-sensitive elements such as ruthenium or osmium in terms of processing temperature. Operation is not desirable for the batch principle because of the high labor costs involved and if the removal contains significant amounts of elements exothermically reacting with sulfuric acid, temperature control becomes difficult and there is a risk that the hot slurry will overboil.

It has now been found that materials containing parent metals and precious metals can be sulfated on a large scale. The invention relates to a process for sulphating a material containing at least one parent metal which forms a water-soluble sulphate by heating a slurry of the material in sulfuric acid at 140 to 250 ° C. The method according to the invention is characterized in that the material slurry and the at least 60% sulfuric acid solution are introduced into a vessel equipped with insoluble electrodes, an alternating current is connected between the electrodes, which heats the slurry through a sulfuric acid solution by resisting, converting most of the parent metal to sulphate. the parent metal is recovered from the aqueous solution.

The invention will be described with reference to the accompanying drawing, in which the figure schematically shows an apparatus with which the method according to the present invention can be carried out,

The slurry of finely divided material and concentrated sulfuric acid solution is passed to a boiler equipped with at least one pair of electrodes so that the electrodes are at least partially immersed in the sludge. An alternating current is applied between the electrodes and through the slurry to heat the slurry by means of a resistance to 140 to 63598 3 250 ° C to sulphate the parent metal. The sulfated slurry is then added to the aqueous medium to dissolve the parent metals to give an aqueous solution of the parent metals from which the parent metal can be recovered.

Most materials containing at least one sulfatable parent metal selected, e.g., from the group consisting of nickel, cobalt, iron and zinc, and preferably at least one noble metal (such as silver, gold, platinum, palladium, osmium, ruthenium, rhodium and iridium ) can be treated by the method of this invention. The parent metal may be in the form of a metal, sulfides or oxides, or mixtures thereof. Thus, materials suitable for treatment include sulfide and oxide ores, ore concentrates, smelting and metallurgical intermediates, scrap metal, extraction residues and electrolyte sludges. Preferably, the material contains only small amounts of acid-soluble by-products, such as magnesium oxide, alumina and calcium oxide, because the value of these components does not correspond to the cost of acid. Furthermore, these components can react to form difficult-to-remove precipitates on the reactor walls. for precious metals, which residue can be treated by known methods to recover the precious metals separately. To simplify the description of the present invention, a method for treating anode sludges is described.

Although coarse materials (particle size greater than 0.37 mm) can be sulfated by the process of this invention, it is preferred to treat materials whose particles pass 100% through a sieve having a mesh size of 0.37 mm, preferably 0.147 mm. In addition to obtaining higher reaction rates, the finer material is easier to handle and keep in a suspended state and a more complete reaction is ensured, reducing the possibility of sulphate stopping the reaction from surrounding coarse particles containing large amounts of unreacted parent metal.

4,63598

The anode slurries are mixed with concentrated sulfuric acid, e.g. solutions containing at least 60% sulfuric acid. Preferably the solution contains at least 80% sulfuric acid and very preferably at least 90% sulfuric acid, so that (1) disproportionate amounts of water do not need to be evaporated, (2) higher acid concentrations have higher resistances, allowing lower current and higher voltage, thus reducing electrical costs and (3) the solutions are more oxidizing, making the sulfatoin process more efficient. Anode sludges can be mixed with sulfuric acid at widely varying sludge densities. For example, anode sludges can be mixed with concentrated sulfuric acid to obtain sludges containing only 10% solids and up to 50 wt% solids. Preferably, the anode slurries are mixed with sufficient amounts of concentrated sulfuric acid to give a weight ratio of sulfuric acid to anode slurry of 1.5: 1 to 6: 1, e.g. 1.8: 1 to 3: 1, depending on the amount of parent metals to be sulfated.

The slurry of anode sludge and sulfuric acid is then fed to a boiler with insoluble electrodes, to be described later, and heated to sulfation temperatures by passing an alternating current between the electrodes and through the sludge, causing the sludge to heat up. Sulfation is performed at temperatures of 140-250 ° C to give rapid and substantially complete sulfation. Although the above temperature range can be used for most materials, it is preferable for some materials to use a lower sulfation temperature. For example, when sulfating sludges containing nickel and copper parisulfides obtained from sulfide anodes, temperatures of 140 to 180 ° C, e.g., 150 to 160 ° C, are used to achieve rapid sulfation while minimizing the loss of ruthenium in the extraction solution or the loss of osmium in the exhaust gas as tetroxide. At these temperatures, most parent metal sulfides are sulfated, releasing elemental sulfur from the sulfide in the feedstock, while the noble metals remain substantially unchanged. When treating nickel and copper slurries from metal anodes, sulfation temperatures of 190 to 235 ° C are preferably used to make the rate of sulfation of the metal and oxide particles of the slurry technically acceptable, again without substantially affecting the precious metals.

63598

To ensure rapid and complete sulfation, the slurry of anode sludge and sulfuric acid is preferably mechanically mixed to provide good liquid-solid contact. Although the amount of mixing is difficult to determine, the mixing should be at least sufficient to keep the solids in suspension. Sometimes, especially when the materials to be treated are relatively coarse, a stronger agitation may be useful in removing sulfates formed on the surface of the particles, exposing fresh surfaces that allow the sulfation reaction to continue.

Sulfation can be performed as a batch process, but the batch size should be kept small because it is difficult to adjust the electrical properties (resistance) of the bath and the use of deep baths results in excessive current requirements at low voltage, resulting in uneconomical capital costs for electrical equipment. Preferably, the sulfation is carried out continuously so that the sludge is fed into and removed from the boiler at a constant rate, which is adjusted so that the reactions are allowed to proceed substantially to completion. When the process is carried out continuously, the size of the boiler and the slurry feed and discharge rate are selected to ensure a substantially complete reaction, and the shape of the boiler may be cylindrical, similar to an electric arc furnace, or shaped to provide flow characteristics. Whatever form of boiler is chosen, it should be designed to minimize feed shortcut and through, thereby providing substantially equal residence time of reactive solids and liquids in the reactor.

After the sulfation is substantially complete, the slurry is preferably allowed to overflow from the sulfation boiler to the water bath to dissolve the sulfated metals. The slurry to water ratios are selected so that the resulting solutions contain substantially all of the metal soluble by sulfation at an acceptable rate.

When the dissolution of the sulfated metals is substantially complete, the residue, which may contain side rock, precious metals, liberated elemental sulfur, unreacted metals, either in the form of metals or compounds, is separated from the metal mother liquor by well known liquid-solid separation methods such as filtration, hydrocyclone, etc.. - 63598 6 recovered, either sequentially or in combination with the mother liquor, by any well known method such as ion exchange, liquid extraction, hydrogen sulfide precipitation, electrolysis, evaporation and the like.

The drawing schematically shows a device which can be used in the practical application of the method according to the present invention. The device comprises a boiler 10 made of carbon steel 12 lined with suitable acid-resistant masonry 14 and a glass-lined carbon steel lid 16 fixed to the boiler 10 by flanges 18 and bolts 20.

The sulfuric acid anode sludge sludge is fed to the boiler 10 via a stainless steel feed pipe 22 and kept in suspension by a mixer 24. The reacted sludge is removed from the boiler 10 via a graphite overflow pipe 26 covered with a ceramic, metal covered pipe 28 . The boiler 10 is provided with a tantalum-lined flow tube 38, which is kept free of solids by a pin 40 and is closed outside the boiler by a polytetrafluoroethylene-lined valve 42. Any gases such as sulfur dioxide and steam are removed from the boiler 10 through the valve 34 for other uses. The temperature of the slurry is measured by a thermocouple 32, and the slurry is held either manually or automatically at a predetermined point by a 3-phase alternating current between the three graphite electrodes 36, only one shown in the figure, immersed in the slurry.

In order that those skilled in the art may gain a better understanding of the invention, the following illustrative examples are provided:

Example I

The anode sludge obtained from the sulfide anodes by electrolysis refining, the composition of which is given in Table I and whose particle size was 100% less than 0.147 mm, was slurried 4 times with its own weight in 93% sulfuric acid. The slurry was fed to a reactor similar to that shown in Figure 1, and the slurry was heated at 150 ° C by alternating current applied to carbon electrodes. The slurry was maintained at this temperature for two hours and then removed to water. After liquid-solid separation, the analysis of the extraction residue was tabulated.

II

7 63598 where I issued. The results shown in Table I show that most of the parent metals in the anode fluids can be sulfated in a single treatment, thus avoiding the multiple sulfation steps that are characteristic of conventional practice.

Table I

Sample% Cu% Ni% Co% Fe% KR *% S °

Found 21.75 7.00 0.59 14.5 23.4 8.5

Extraction residue 1.50 0f82 0.20 1.78 41.6 42.4 * total sulfur

Example II

The anode sludge obtained from the bladder copper anodes in electroplating refining, the composition of which is given in Table II and whose particle size was 100% less than 0.246 mm and a substantial part of which passed through a sieve with a mesh size of 0.061 mm, was slurried 1 to 8 to 2.5 times its own weight 30% water.

Table II

Sample Cu Ni Other elements present

Sludge 21.35% 22.16% It, Te, Pb, 02, Ag, Au and small amounts of precious metals

The slurry was fed continuously at a rate of 1150 kg / hr to the reactor boiler illustrated in Figure 1. It was heated to 215 ° C and continuously removed to a water bath in which most of the copper and nickel dissolved and separated by conventional methods. Only small amounts of selenium and tellurium and a few other metals dissolved. These were removed quantitatively by sequential and conventional precipitation treatment, leaving only copper and nickel in solution. Sulfation of the anode sludges as described above converted about 98% of copper to copper sulfate and 95-97% of nickel to nickel sulfate, which sulfates were recovered by extraction with water.

Claims (5)

8 63598 A process for sulphating a material containing at least one parent metal which forms a water-soluble sulphate by heating a slurry of the material in sulfuric acid at 140-250 ° C, characterized in that the slurry and at least a 60% sulfuric acid solution are introduced into a container of insoluble electrodes, electrodes an alternating current is connected, which, as it passes through the sulfuric acid-containing solution, heats the slurry by resisting, converting most of the parent metal to sulfate, the sulfated slurry is extracted with water, and the sulfated parent metal is recovered from the aqueous solution. Method according to Claim 1, characterized in that the slurry consists of anode sludge. Process according to Claim 1 or 2, characterized in that the sulfuric acid solution contains sulfuric acid in such an amount that the weight ratio of sulfuric acid to anode sludge is 1.5: 1 to 6: 1. Process according to one of Claims 1 to 3, characterized in that the slurry consists of a precious metal-containing slurry formed by the electrolysis of nickel sulphide or copper sulphide anodes and is heated at 140 to 180 ° C. Process according to one of Claims 1 to 3, characterized in that the slurry consists of a precious metal-containing slurry formed by the electrolysis of nickel metal or copper metal anodes and is heated at 190 to 235 ° C.