LEACHING OF METALS FROM LATERITE USING ACIDIFIED SODIUM THIOSULPHATE AND RECOVERY OF NICKEL FROM LEACHED LIQUOR.

Abstract

Laterite samples were collected from a laterite deposit opposite the North Gate of the Federal University of Technology, Akure. The samples were dried, ground and sieved into different particle sizes. The samples were pre-analyzed using X-ray fluorescence and atomic absorption spectrophotometer for elemental compositions, and X-ray Diffractometer for structural composition. Physicochemical properties such as; moisture contents, loss of mass on ignition and pH were determined. Leaching process was carried out when 5 g of laterite sample was added into 100 ml of mixture of sodium thiosulphate and hydrochloric acid taken into consideration the effects of concentrations of hydrochloric acid and sodium thiosulphate, the effects of particle sizes, time and temperature. Solid-liquid separation was carried out after which the liquid was taken for atomic absorption spectrophotometer analyses. Hydrochloric acid and sodium thiosulphate concentration were studied over the range of 0.1-2.0 M, as 10.7 % Ni and 2.1 % Fe were extracted at 0.1 M hydrochloric acid which increased to 18.7 % Ni and 5.8 % Fe when 2.0 M was used. The extraction of nickel increased from 11 % to 33.3 % when the concentration of sodium thiosulphate was increased while the extraction of iron barely increased from 1.1 % to 4.2 %. The extraction of nickel decreased from 41.6 % to 13.5 %, as that of iron decreased from 5.7 % to 2.3 % as the particle size increased. The leaching temperature used range from 50-80 °C, and the metal extracted increased from 6.7 % Ni and 0.6 % Fe at 50 °C to 25.3 % Ni and 4.2 % Fe at 80 °C. Nickel was recovered by using alcoholic dimethyl-glyoxime (DMG) and ammonia was used to adjust the pH, 98.2 % Ni extraction was obtained among the pH value of 4-8 at pH 7, while 98.8 % Fe extraction was obtained at the same pH. It is therefore recommended that the recovery process should be performed at pH 7. The kinetics of the leaching was calculated and it showed that the leaching data fitted Avrami model. The initial leaching rate is infinite and the rate continually decreases with time.