Caracterização e lixiviação atmosférica com ácido sulfúrico de minériolaterítico de níquel de depósito brasileiro

Abstract

Nickel lateritic ores have gained prominence as the main source for the metal. The processing by techniques that present lower costs has encouraged research in the field of atmospheric leaching for ores that the application of hydro and pyrometallurgical processes are not efficient. In this work a northern-Brazilian sample of lateritic ore characterized by large amount of fine particles (d50 75m and 40wt.% of the materialbelow 38mm) and high specific surface area (up to 72 m2/g). Chemical analysis showed a trend of Ni and Fe concentration in the finer fractions (-75m sample 4-L) and of Si and Mg in the coarsest size range (-500 ± 150m sample 2-L). The ore is composed by quartz (27,3%), hematite (7,2%), magnetite (4,8%), chromite (6,0%), chlorite (21,8%) and goethite (28,1%).Goethite and chlorite is the main nickel bearing minerals in the ore. The ore contains 1.63% (Ni), 29.2% (Fe), 16.8% (Si), 3.61% (Mg),0.103% (Co) and 0.525% (Mn). Fractionated samples had levels of 2.06% Ni and 35.6% Fe (4-L) and 19.3% Si and 3.64 Mg (2-L). According to the parameters evaluated in the atmospheric leaching, no influence of agitation (200 and 400rpm) was verified on the metals extractions. Design of experiments was carried out to evaluate the temperature (65 and 95°C), initial acid concentration (0.11 to 0.90mol/L) and solidliquidratio (10 to 30%w/w). Sample 4-L presented significant results for nickelextraction over the three factors evaluated, meanwhile for sample 2-L the acid concentration and solid-liquid ratio were significant for nickel extraction. The highest extractions obtained by the design of experiments were 47% (Ni), 34% (Fe), 65% (Mg), 53% (Co) e 67% (Mn), for sample 4-L, and 61% (Ni), 32% (Fe), 83% (Mg), 40% (Co) e 58% (Mn), for sample 2-L under conditions of 95°C, 10%w/w solid-liquid ratio, 0.90mol/L H2SO4 and stirring rate at 400rpm. Sample 4-L is, therefore, limiting theprocess and was evaluated under more drastic acid conditions (up to 2mol/L) where the extraction and concentration of elements reached 59% and 2,3g/L (Ni), 54% and 36,8g/L (Fe), 76% and 4,9g/L (Mg), 58% and 106mg/L (Co), 74% and 561mg/L (Mn) with acid consumption of 700kg/t and residual free acid of 53g/L, at 95°C and 15%w/w. Investigations with the global ore were also carried out and the results were more promising, with higher extractions and also lower acid consumption. The kinetic modelling indicated leaching control is done by diffusion through the ash/pore layer in the initial minutes (60 minutes) and by reaction or diffusion through the pore layer in the final minutes (60-240 minutes). The activation energies for the extraction reactions were greater than 40kJ/mol for Ni and Fe, and between 40 and 20kJ/mol for Mg and Co