Optimum condition for the removal of Cr(VI) or total Cr using dried leaves of Pinus densiflora

A novel biomass, dried leaves of Pinus densiflora, showed very good performance in removing mutagenic Cr(VI) from aqueous solution in this study. Analytical results for different chromium species in aqueous and solid phases indicated that the mechanism of Cr(VI) removal by the biomass was 'adsorption-coupled reduction'. Among various parameters of batch operation, pH, temperature and contact time significantly affected Cr(VI) removal and total Cr removal individually. As a result, optimal condition for the Cr(VI) removal was not equal to that for the total Cr removal. To examine the individual effects of these parameters on the Cr(VI) and total Cr removals statistically, therefore Box-Behnken model for experiment design and second-order polynomial model for fitting experimental data were used in this study. The removal efficiency of Cr(VI) increased with a decrease in pH or with increases of temperature and contact time until equilibrium had been attained. Meanwhile, an optimum pH existed for the total Cr removal efficiency, but increased with the increases of temperature and contact time. With 60. h of contact time, 100% of Cr(VI) removal and > 95% of total Cr removal could be obtained at pH 4 and 40°C.