Hi Lizeng The ore processing for laterite ore is actually in the mining process world quite complex, the ore processing is very expensive in maintenance and running costs. This is offset by the ease of mining and milling. Mining is very shallow pit generally max depth 40-50 metres then off to crusher which is the the most basic of crusher called a sizer. The sizers only have to break up very soft product not hard rock as in most other metals, hence much less crusher maintenance. Then it goes to a mill which has been called scrubber as it has very limited balls for grinding and its main job is to add water to make a slurry of generally SG of 1.29 to 1.34 as feedstock for autoclaves. This slurry goes to big agitated holding tanks as storage for autoclaves. The slurry in feed to the claves via preheating tanks take takes temperature up to 190degC using steam a heating agent then fed to autoclaves via positive displacement pumps at a pressure of depending on clave design of 4000 to 6000Kpa, this is fed in not continuously but as clave discharges last compartment of processed ore. The autoclave is maintained at 250degC and pressure as previously stated 4000-6000Kpa (570psi- 860psi) the pressure is required for reaction and to also stop ore vaporising at the high temps. 100% sulphuric acid is added into clave at same time at rate generally of 1 tonnes acid to 10 tonnes of slurry. Hence very expensive in acid terms avg price of acid $250 per tonnes. This is why is most laterites plants include acid plant as part of design. The acid plant can then also supply the steam to heat ore and clave and also pressurise clave ,xcess steam can be used to drive steam turbines to supply free power (acid plants are basically big steam generators as well as supplying acid). The claves have 6 cascading compartments which gives the retention times to dissolve nickel and cobalt into solution.When the last compartment is dicharged it goes into a series of flash chambers to dissipate pressure from the before mentioned pressures down to atmospheric as the pressure dissipates temp falls back to 95degC.
The slurry is then, in all other laterite plants, sent to CCD,s (Counter Current Decantation) basically big thickeners to concentrate product (get rid of most of the mud) the sent to filters to separate waste metals such as iron , copper , magnesium, copper from slurry. These are not in commercial quantities and are discarded. The product then goes to SX decks (solvent extraction ) where a petroluem product generally a kerosene product separates the nickel and cobalt into separate solutions , this is done via quite a number of separate cells . This gives you the blue and purple solutions which are dried to have the separate sulphatescrystals.
There is no smelter and refinery process required as this is only used when you are supplying nickel and cobalt metal powders or briquettes. To do this requires more autoclaves at lower pressures and temps injecting ammonia to take the wet metal out of the suspended state in the solution.
Hope this answers your question about the processing, I tried to simplify it as much as possible.
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