Nickel ores, ammonia leaching

HydrometaHurgical Processes. The hydrometaHurgical treatments of oxide ores involve leaching with ammonia or with sulfuric acid. In the ammoniacal leaching process, the nickel oxide component of the ore first is reduced selectively. Then the ore is leached with ammonia which removes the nickel into solution, from which it is precipitated as nickel carbonate by heating. A nickel oxide product used in making steel is produced by roasting the carbonate. 

Nevertheless, manganese nodules can, at best, be considered to be similar to land-based nickel laterites, and consequently most of the processing techniques that have been tried are similar to those used on lateritic ores. Reduction roasting followed by ammonia leaching, as in the Nicaro process, and high-temperature sulfuric acid leaching, as in the Moa Bay operation, have been extensively tried to process nodules. 

Trace the steps in the production of high purity nickel metal from crude sulfide ore (a) by the Sherritt Gordon ammonia leach process, (6) by the Mond process, and (c) by acid leaching. 

Hydrometallurgical treatment of lateritic ores, by the reduction roast/ammonia leach process is one of the methods used for the recovery of nickel from low grade lateritic ores. In a recent study Chander and his associates (19, 20) used such... 

Laterite ores must first be reduced. The reduced ore is leached with an ammonia-ammonium carbonate solution. Nickel dissolves as nickel amine. The saturated solution is heated by steam, ammonia is driven off, and nickel is precipitated as a basic carbonate. 

The other major group of solutes recovered by leaching are minerals. Gold is recovered from low-grade ores with aqueous sodium cyanide. Copper is recovered by leaching the ore with acid and then extracting the dissolved copper with kerosene solutions of oximes. Nickel can be leached with combinations of sulfuric acid and ammonia. 

HydrometallurgicalProcesses. HydrometaHurgical refining also is used to extract nickel from sulfide ores. Sulfide concentrates can be leached with ammonia (qv) to dissolve the nickel, copper, and cobalt sulfides as amines. The solution is heated to precipitate copper, and the nickel and cobalt solution is oxidized to sulfate and reduced, using hydrogen at a high temperature and pressure to precipitate the nickel and cobalt. The nickel is deposited as a 99 wt % pure powder. 

Lateritic Ores. The process used at the Nicaro plant in Cuba requires that the dried ore be roasted in a reducing atmosphere of carbon monoxide at 760°C for 90 minutes. The reduced ore is cooled and discharged into an ammoniacal leaching solution. Nickel and cobalt are held in solution until the soflds are precipitated. The solution is then thickened, filtered, and steam heated to eliminate the ammonia. Nickel and cobalt are precipitated from solution as carbonates and sulfates. This method (8) has several disadvantages (/) a relatively high reduction temperature and a long reaction time (2) formation of nickel oxides (J) a low recovery of nickel and the contamination of nickel with cobalt and (4) low cobalt recovery. Modifications to this process have been proposed but all include the undesirable high 760°C reduction temperature (9). 

Nicaro [named after the Cuban town] A process for extracting nickel from low-grade ores. The ore is reduced by heating with producer gas and is then leached with aqueous ammonia. 

In the Nippon Mining Company process,163 the aqueous feed consists of a solution of cobalt, nickel and other metal sulfates obtained by the high-pressure oxidative leaching of a mixed metal sulfide ore. Following the removal of iron and copper by chemical precipitation methods, and the successive extraction of zinc and cobalt by organophosphorus acid reagents (Section 63.3.2.2) under weakly acidic conditions, the pH value of the solution is adjusted to between 9 and 9.5 with ammonia, and nickel is extracted into a 25% solution of LIX 64N in an alkane solvent. 

This study was carried out on a limonitic laterite from New Caledonia. The main objective was to evaluate the atmospheric leaching of the ore in ammonium sulphate media using ferrous sulphate as reductant. Different parameters were examined, such as total ammonia concentration, temperature and ferrous sulphate concentration. At 80 C, 130 g/1 of total ammonia, 2.73 g FeS04/ g ore and pH 8.2, nickel extraction was 64 % while 20 % of cobalt remained in solution after 8 hours. 

Results obtained from the present research suggest the limonitic laterite can be partially reduced by ferrous sulphate. Maximum nickel extraction was 64% at SO C, 2.73 g FeS04/ g of ore, 130 g/1 total ammonia in 10 hours. At the same conditions the cobalt and manganese extractions were only 16% and 43%, respectively. The different leaching behavior between nickel, cobalt and manganese is due to the fact that they are associated with different mineralogical phases. 

HydrometaUurgical refining can be applied both to laterite ore and sulfide ore or sulfide ore concentrates. Soluble nickel amines are formed during pressure leaching of the sulfide ore concentrate with strong anunoniacal solution at a moderately elevated temperature. The saturated solution is boiled to drive off ammonia and precipitate copper as sulfide. Sulfur is oxidized. Nickel and cobalt are recovered as pure metal powders by reduction with hydrogen under pressure. 

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