Biosorption of Cr (VI) from aqueous solution by Rhizopus nigricans

The study was aimed to quantify the Cr sorption ability of powdered biomass of Rhizopus nigricans at the best operating conditions. The influence of s olution pH, agitation, Cr (VI) concentration, biomass dosage, contact time, biomass particle size and temperature were studied. The optimum pH for bio sorption of Cr (VI) was found to be 2.0. Higher adsorption percentage was n oted at lower initial concentrations of Cr ions, while the adsorption capac ity of the biomass increased with increasing concentration of ions. Optimum biomass dosage was observed as 0.5% (w/v). More than 75% of the ions were removed within 30 min of contact and maximum removal was obtained after 8 h . Biomass particles of smaller size (90 um) gave maximum adsorption (99.2%, ) at 100 mg/l concentration. The adsorption capacity increased with increas e in temperature and agitation speed and the optimum were determined as 45 degreesC at 120 rpm. Freundlich and Langmuir isotherms were used to evaluat e the data and the regression constants were derived. The adsorption rate c onstant values (K-ad) were calculated for different initial concentration o f Cr ions and the sorption was found to be higher at lower concentration (1 00 mg/l) of metal ion. (C) 2001 Elsevier Science Ltd. All rights reserved.