چكيده به لاتين
Recently, the recovery of nickel from lateritic resources has been increasingly drawing the attention of researchers. Nickel laterites are of two types of saprolitic, which is relatively high-grade, and limonitic that is of low-grade. The processing of low-grade ores is more challenging, so that a physical or chemical beneficiation step is usually needed before the usual extraction process. Carbothermal reduction is considered a suitable pyrometallurgical method for the extraction of nickel from laterites, in which iron and nickel are selectively reduced at temperatures below the melting point of the reaction mixture, and then separated from the gangue by physical methods such as magnetic separation. In the present research, carbothermal reduction has been performed on a nickel concentrate obtained from a domestic low-grade limonitic laterite via a novel hydrometallurgical treatment developed by Asadrokht and Zakeri. The concentrate contains 3.7% nickel and 4.8% iron in the form of oxalate compounds. A Central Composite Design (CCD) approach was used to investigate the effect of temperature, time, amount of reductant and dosage of calcium chloride additive, while nickel and iron recoveries as well as particle size and grade of ferronickel product were served as response variables. It was realized that the reaction product should be quenched or cooled under non-oxidizing conditions to prevent the formation of nickel ferrite. Reaction temperature was found to be the most important influential factor. Calcium chloride was able to increase the particle size of ferronickel to some extent by increasing iron recovery and creating local liquid phase in the sample. The grade of ferronickel was 60% on average, which is much higher than the grade obtained from the reduction of the primary laterite ore and more desirable for steelmaking purposes. From statistical analysis of the results and fitting proper models for each response, optimal conditions were determined with different targets. In one case targeted for magnetic separation, 85% recovery of nickel, 46% recovery of iron and 1.7 µm particle size of ferronickel was achieved. In a different case suitable for melting separation, 93% recovery of nickel and 42% recovery of iron was obtained.