Transport of humic and fulvic acids in relation to metal mobility in a copper-contaminated acid sandy soil.

Abstract

The transport of inorganic and organic pollutants in water and soil can be strongly influenced by the mobility of natural dissolved organic matter (DOM). In this paper, the transport of a humic acid (HA) and a fulvic acid (FA) in a copper-contaminated acid sandy soil was studied. The data showed that the transport behavior of HA differed from that of FA. The breakthrough curves (BTCs) of HA were characterized by a rapid relatively sharp front followed by a plateau at a lower HA concentration than in the influent solution. The increase of the Ca concentration decreased the HA concentration further. Compared to HA, the BTCs of FA were retarded and showed an extended tailing, approaching complete breakthrough. The increase of the Ca concentration decreased the FA concentration only temporarily. On the basis of our model calculation, the characterization of HA transport could be explained by the coagulation of HA largely upon the binding of Al. The increase of the Ca concentration resulted in further coagulation of HA because of the increased Ca adsorption, which occurred mainly in the Donnan phase. For FA, the adsorption to the soil matrix was more likely the process that controls its solubility and mobility. The mobility of Al and Cu in the soil column was closely related to the solubility and transport of the DOM in soil solution. The concentration of Ca in the effluent was lower than in the influent because Ca was retained in the soil due to the retardation of HA and FA and due to the compensation of the other cations released from the soil to the solution.