Abstract
The removal of chromium(III) from leather solid waste was carried out by two steps: the leaching step and the ion exchange step. Orthogonal method was applied to the leaching process with H2SO4 as leaching agent and the leaching rate was nearly 100%. The adsorption and desorption of Cr3+ with 732# cation exchange resins were investigated in the ion exchange process. The effects of the resin types, temperature, rotating speed, liquid-solid ratio, initial Cr3+ concentration and time were investigated and the optimum conditions were as follows: 732#, 333 K, 120 r/min, 20 ml/g, 280 ppm and 5 h. The removal efficiency of Cr3+ from leather hydrolysate was over 95% under optimized conditions. The desorption efficiency of Cr3+ from loaded resins was almost 99% by three times cross-flow with Na2SO4 solution. The re-adsorption of Cr3+ could achieve 95% by regenerated resins. The adsorption isotherms, kinetics and thermodynamics of Cr3+ onto 732# resins were investigated. The adsorption process appeared to follow Langmuir isotherm model and the pseudo-second-order kinetic model. △H0 = 33,816.03 kJ/mol and △S0 = 141.35 J/(mol·K) were calculated. The two-step method was proved to be a sustainable and economic method for separating chromium from leather waste.
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