Adsorption-Desorption Studies of Selected Chlorophenols and Herbicides and Metal Release in Soil Mixtures with Fly Ash

Abstract

The influence of fly ash on the adsorption and desorption of four selected chlorophenols and two herbicides has been studied in mixtures with a sandy clay loam (SCL) soil. Fly ash and soil mixtures with a range of fly ash content from 0 to 30% were used to study adsorption and desorption of four chlorophenols, 2,4-DCP, 2,4,6-TCP, 2,3,5,6-TCP and PCP as well as two selected herbicides, alachlor and metolachlor, in batch experiments. The linear isotherms indicated a constant partition of chlorophenols and herbicides between the bulk solution and mixtures of fly ash and soil, for a concentration range from 0.025 to 0.2 mg l−1 for chlorophenols and 0.1 to 10 mg l−1 for herbicides. Mass balance estimations show that the adsorbed amounts of chlorophenols in mixtures of soil with 30% fly ash content, are up to 36.5% for 2,4-DCP, 55.8% for 2,4,6-TCP, 68.7% for 2,3,5,6-TCP and 84.9% for PCP and the respectivelly adsorbed amounts of herbicides in mixtures with 20% fly ash are up to 37.5% for alachlor and 43.2% for metolachlor. In contrast, the amounts of desorption decrease as the fly ash content and the number of chlorines in the phenolic ring increase. Results of leaching tests of metals from soil mixtures with fly ash have shown that as the fly ash content and pH values increase, the concentration of Mg, Mn and Fe decrease in the aqueous solutions by metal precipitation. The concentrations of Ni, Cu and Zn remain at low levels and the concentration of Cr increase due to the formation of more soluble metal species at high pH values.