Recently there has been a lot of interest in using PAL (Pressure Acid Leach) tec

Question

Recently there has been a lot of interest in using PAL (Pressure Acid Leach) technology to recover nickel from laterite ores (these are complex oxide ores containing in addition to nickel (as NiO), iron (as goethite FeOOH), aluminum (as Al2O3), Mg (as MgO) and Si (as SiO2)). This technology involves treating the ore with concentrated sulphuric acid at temperatures up to 270C in large continuously operating horizontal autoclaves. You are given that an ore containing 1.5 wt %Ni (as NiO) is fed to the pressure leach autoclave at 5,000 TPD (tonnes/day) with sulphuric acid solution fed at 6,000 TPD. Nickel extraction is 90% into the leach solution which is being produced at 6,500 TPD. Calculate:

(a) The % solids in the leach feed, and
(b) The weight % Ni in the leach residue. Assume solids weight decreases by 10% during the leach.

Explanation / Answer

a)
per day, solid fed = 5000 tomes
sulphuric acid fed = 6000 tomes
% solid = solid fed / (total feeding)
             = (5000)*100 / (5000+6000)
             = 45.45 %
b)
NiO fed = 1.5% of 5000 = 75 tones
Mass of Ni fed =75*molar mas of Ni /molar mass of NiO
                           = 75*59/75
                           = 59 tonnes
Ni converted =90% of 59 tonnes =53.1 tonnes
Ni in residue = 59-53.1 = 5.9 tonnes
Total weight = 90% of 5000 + 6000 =10500 tonnes

% of Ni = 5.9*100/10500 = 0.056 %

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