Influence of pH on Cr(VI) reduction by organic reducing substances from sugarcane molasses

The remediation of Cr(VI) is one of the hot issues in groundwater pollution remediation. The influences and effects of pH on Cr(VI) reduction by organic reducing substances in sugarcane molasses were studied under the sterilization and unsterilization conditions by means of batch laboratory-scale experiments. The results showed that pH of reaction solution has a great influence on the reduction of Cr(VI) by sugarcane molasses. When pH >= 3.0, the final removal efficiency of Cr(VI) on the condition of sterilization and unsterilization at pH values of 8.0, 5.8, 4.0 and 3.0 was 15.441%, 17.945%, 29.205%, 36.258% and 99.236%, and 98.577%, 99.235% and 99.368%, respectively. When pH < 3.0, the final removal efficiency of Cr(VI) on the condition of sterilization and unsterilization at pH values of 2.5 and 2.0 was 99.631% and 99.895%, and 99.631% and 99.895%, respectively. The main mechanism involves chemical reduction and biological reduction. And biological reduction in the process of Cr(VI) reduction by sugarcane molasses is of the first priority when pH >= 3.0; when pH < 3.0, the rate of chemical reduction was higher and it was not the basic existing biological reduction. The relationship between pH and pseudo-first-order rate constant (k(obs)) on both the sterilization and unsterilization conditions was satisfied with Boltzmann model. There is an inflection point at the pH of about 2.6, which also indicated the influence mechanism of pH on the reduction of Cr(VI) by sugarcane molasses.