Optimization and Kinetic Modeling of the Removal of Lead from Enugu Coal by Acid Leaching

Removal of lead from Enugu coal with different acids as the leachant under different conditions such as leaching time, particle size, acid concentration, and leachant volume was investigated in this studies. The filtrate from each treatment was analyzed with Atomic Absorption X-ray Spectrometer (AAS) to determine the amount of lead leached. Nitric acid was found to be the best acid for the leaching of lead from Enugu coal. Kinetic studies carried out showed that the dissolution rate increased with: decreasing particle size, increase in stirring speed, acid concentration and leaching temperature. The experimental results revealed that the dissolution rate is a chemical reaction controlled via hydrogen ion concentration [H+], with reaction order of 0.9 and the reaction kinetics can be expressed as 1-(1-X)1/3 =2.566x10-4(CHNO3)0.86 (dp).992 (L/S).44 (SS).049 exp(53.49/RT). A quadratic model was predicted and optimized using second order orthogonal design (Box-Benken) which resulted in Particle size of 40µm, reaction time of 8.5 hours, and HNO3 concentration of 2mol/dm3. The optimum conditions were validated at model desirability of 1. Experimental value of 96.39% with error of 0.530% was removed.