Precipitation of Nickel Hydroxide from Simulated and Atmospheric-leach Solution of Nickel Laterite Ore

Mixed Hydroxide Precipitate (MHP) is one of intermediate products of nickel laterite ore processing through hydrometallurgical route. This type of product can be further treated in Caron Process and/or atmospheric acid leaching to produce separate pure nickel and cobalt. In the present work, precipitation behaviour of nickel hydroxide from artificial and pregnant leach solution of Indonesian nickel laterite ore is discussed. The effects of pH, temperature, seed addition, types of neutralizing agents (i.e. NaOH, NH3 and MgO) on the nickel precipitation percentage, activation energy and the constant rate of nickel precipitation were investigated. The kinetics study was done in artificial solution which contains adjusted nickel, cobalt and iron concentratio n. Product characterization was performed by chemical composition, particle size distribution, SEM-EDX, and XRD analysis. The highest nickel precipitation percentage of 99.9was obtained from the precipitation under pH of 9 at 50 °C. The addition of seed material promotes nickel precipitation at lower supersaturation through heterogeneous nucleation. The type of neutralizing agent for pH adjustment has some influence on the percentage of nickel precipitation. The use of MgO as neutralization agent exhibi ted a better percentage of nickel precipitation and precipitation kinetics than NH3 and NaOH. It is suggested that MgOslurry as neutralizing agent gives a seeding effect on nickel hydroxide precipitation that is not fulfilled by the other two types of neutralizing agent. SEM analysis result indicated that by aggregation of smal l particles occurs during the formation of nickel hydroxide precipitate.