Kinetics of chromium removal from spent tanning liquors using acetylene production sludge

The removal of Cr(III) present in spent leather tanning baths by precipitat ion with acetylene production sludge (APS) is studied. The hydroxide and ca rbonate contents in APS were 1.05 and 0.10 g of CaCO3/g of dry sludge, resp ectively, and the Cr concentration in the tanning bath was 2467 mg/L. The e xperimental work was carried out at 15, 20, 25, 30, and 35 degreesC using A PS samples of different grain size (89,178, and 356 mum). Percent removals after 180-min reaction time using 356-mum APS particles range from 99.0 to 99.9 as temperature increased from 15 to 35 degreesC. Similar or higher rem oval rates are obtained when using smaller APS particles. Chromium removal efficiencies using APS as precipitant are comparable with those obtained wi th NaOH, CaO, or MgO. The Cr conversion X increases with time t and is rela ted to the particle radius and the absolute temperature T by the expression X/1 - X = r(0)(-0.22) exp((45.45-13401/T))t. The average activation energy for the reaction is 111.4 kJ mol(-1). Despite some deviations observed for the finer particles and the lower temperature (15 degreesC), the model des cribes adequately the results obtained for all APS particle sizes at 20 deg reesC.