Cr(VI) reduction capability of humic acid extracted from the organic component of municipal solid waste

The capacity of humic acid extracted from organic waste (HAw) to reduce Cr(VI) was tested at pH 2.5, 4 and 6 and compared with coal-derived humic acid (HAc). HAw was more effective than HAc in reducing Cr(VI). The kinetics of Cr(VI) reductions depended strongly on pH. The calculation of the apparent rate coefficients indicated that HAw was more efficient at reducing Cr(VI) than HAc, but was also more efficient than HAs from soil and peat. The reduction capability of HAs depends on the type of functional groups (i.e., thiols and phenols) present, rather than the free radicals. HAw was more efficient at reducing Cr(VI) than HAc because more reactive phenols were present, i.e., methoxy- and methyl-phenols.