Dechlorination of chlorophenols by magnesium-silver bimetallic system.

More than 85% of 10 mg L(-1) of pentachlorophenol (PCP) was removed by magnesium/silver (206/1.47 mM) bimetal system in the presence of acetic acid. Dechlorination was found to be sequential and phenol was identified as the ultimate hydrocarbon skeleton along with some accumulation of tetra-, tri-, and dichlorophenols. The dechlorination reaction was found to follow second-order kinetics. Lower PCP removal efficiency (35%) was observed when the reaction was carried out in the absence of acid using Mg(0)/Ag system. When the reaction was conducted using Mg(0) alone in the presence of acid, substantial sorption of PCP occurred with very low efficiency of PCP dechlorination. Dechlorination studies on 10 mg L(-1) initial concentrations of 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and 2,4,5-trichlorophenol (2,4,5-TCP), under identical conditions as to PCP, revealed that dechlorination efficiency and reaction rate constants decrease with decreasing number of chlorine atoms on the target compound. A correlation (R(2)>0.9) between the dechlorination rate constants and E(LUMO) for chlorophenols was obtained.