Page 1 DIRECT ELECTROWINNING OF NICKEL BACKGROUND OF THE INVENTION [0001] This invention relates to the recovery of nickel from a dilute process leach solution. [0002] A pregnant leach solution (PLS), which results from high-pressure acid leaching (HPAL) of laterite ores, generally contains a mix of cobalt and nickel sulphide. [0003] There are two methods by which cobalt and nickel are generally recovered from the PLS, viz. mixed sulphide precipitation (MSP), and mixed hydroxide precipitation (MHP). [0004] During the MSP process, the PLS is purified by removing copper with NaHS before precipitating the mixed nickel sulphide with H 2 S. The process is conducted in an autoclave, at a high temperature and pressure. The mixed sulphide product typically contains about 55 to 60% nickel, which is refined by hydrogen reduction or electrowinning, to produce nickel metal. [0005] Disadvantages associated with the MSP process are that; e it requires the use of H 2 S, which is an expensive and hazardous reagent; and * the autoclave is associated with high maintenance costs and requires well trained personnel to operate. 17/0/385/foreign Page 2 [0006] During the MHP process, limestone is added to remove iron, aluminium and chromium from the PLS. Nickel is then precipitated with magnesium oxide. The MHP product contains about 35% to 40% nickel sulphide, which is refined to produce nickel metal. [0007] Disadvantages associated with this process are; * it requires large recycle streams to minimise nickel and cobalt losses; and * it requires the use of magnesium oxide, which is expensive and requires downstream purification. [0008] Neither the MSP nor the MHP process produces a particularly high quality nickel metal product. Consequently a relatively large quantity of a low grade product has to be transported to a refinery, leading to an overall increase in the cost of recovery. [0009] An object of the present invention is to address, at least to some extent, the aforementioned factors in order to produce a high grade nickel product, with an increased market value, at a reduced operating cost. SUMMARY OF INVENTION [0010] In accordance with the invention a nickel metal product is recovered from a dilute process leach solution (PLS) by direct electrowinning. [0011] The nickel metal product recovered by means of direct electrowinning is of a higher grade, compared to metal products recovered by means of the MSP process and the MRP process. 17/0/385/foreign Page 3 [0012] The leach solution from which the nickel is recovered may result from a high-pressure acid leach process of laterite ores. [0013] Prior to the direct electrowinning of the nickel, iron, aluminium, copper and chromium contained in a pregnant leach solution may be removed by means of any appropriate process. [0014] The invention extends to a method of recovering a nickel metal product from a pregnant leach solution by subjecting the leach solution to direct electrowinning step. [0015] The leach solution from which the nickel is recovered may result from a high-pressure acid leach process of laterite ores. [0016] Prior to the direct electrowinning of the nickel, iron, aluminium, copper and chromium contained in a pregnant leach solution may be removed by means of any appropriate process. [0017] The PLS may be obtained from high pressure leaching of a laterite ore. [0018] Following the direct electrowinning step, lime may be added to the solution to precipitate nickel which is recovered by a solid/liquid separation step. BRIEF DESCRIPTION OF THE DRAWING [0019] The invention is further described by way of example with reference to the accompanying drawings: Figure 1 is a flow sheet of a high pressure leach process of a laterite ore during which a pregnant leach solution is formed; and 17/0/385/foreign Page 4 Figure 2 is a flow sheet of a process for recovering nickel, from the pregnant leach solution of Figure 1, in accordance with the present invention. DESCRIPTION OF PREFERRED EMBODIMENT [0020] Figure 2 of the accompanying drawings illustrates a process 10 in which the method of the invention is utilised. [0021] The process 10 is preceded by a process 10A, illustrated in Figure 1, during which a laterite ore 12 is subjected to conventional ore preparation and preheating steps 14 and 16 respectively, prior to being subjected to a high pressure acid leaching step 18. [0022] During the step 18, sulphuric acid and steam 20 are added to the prepared ore. The ore is then leached in an autoclave at a temperature between 240 0 C to 270 0 C and at a high pressure. [0023] During a subsequent heat recovery step 22, jarosite and hematite are precipitated, resulting in flash steam 24 and a leach pulp 26. The steam 24 is recycled to the step 16. [0024] The pulp 26 is subjected to a counter current decantation (CCD) step 28. Tailings 30 are directed to waste. The pH of the resulting solution is adjusted (step 32), by the addition of limestone 34 to produce a PLS 36 suitable for processing in terms of the invention. [0025] Referring to Figure 2, lime is added to the PLS 36 during a step 38 to precipitate iron, prior to a solid/liquid separation step 40, during which the precipitated iron is removed from the PLS. 17/0/385/foreign Page 5 [0026] In a step 42 additional lime is added to the PLS to precipitate copper prior, to a solid/liquid separation step 44, during which the precipitated copper metal is removed from the PLS. [0027] The step 44 is followed by a direct electrowinning circuit 46, during which nickel 48 is recovered. Some of the solution from the circuit 46 is returned to the HPAL process 10A. The remainder of the solution passes to a step 50 during which lime is added to precipitate nickel, prior to a solid/liquid separation step 52, during which the precipitated nickel is removed from the PLS. A part of the resulting solution is recycled to step 38 and the rest is directed to an effluent treatment stage. [0028] The invention is based on the use of direct electrowinning of nickel as an alternative to nickel recovery by the MSP process and MHP process from a conventional refinery. This holds significant economic value in the production of nickel, particularly at a remote site which may have a high capital investment risk and where there is a need to maximise the nickel content in the final product and hence the value. The nickel which is recovered using the technique of the invention has increased nickel purity compared to the nickel hydroxide product, although it has a lower grade than LME or A grade nickel produced by a nickel refining process. [0029] It is envisaged that nickel recovery by direct electrowinning, as is contemplated by the present invention, would significantly reduce operating costs. [0030] The method of the invention is thus capable of achieving the following: 17/0/385/foreign Page 6 * A higher grade product resulting in corresponding increased revenue; * Reduced transport cost of the higher grade product; * Use of reagents, such as MgO and H 2 S, is eliminated, decreasing the operating costs; * Limiting the use of lime; * Eliminating the use of additives; and * A simplified process for the recovery of nickel metal, which eliminates the use of an autoclave and other operational risks. [0031] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. [0032] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 17/0/385/foreign