KINETICS OF NiS LEACHING IN NITRIC ACID SOLUTIONS.

A study of the rate of dissolution of NiS in nitric acid solutions was carried out by measurement of the rate of formation of nickel ions in solution. The influence of temperature in the range 30-80 degree C, nitric acid concentration (0. 5-3. 0 M) and stirring intensity (100-1000 rev/min) was evaluated. The slowest dissolution stage of NiS in nitric acid solution is related to the chemical reaction on the solid surface; this reaction proceeds in agreement with the value of activation energy equal to 20. 8 kcal/mole. Dissolution rate does not depend on stirring intensity. At acid concentrations lower than 2. 0 M the rate is proportional to acid concentration. The formation of sulfate ions depends on temperature and acid concentration.