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The Effect of Nitrilotriacetic Acid on the Solubilities of Metals in Soil-Sludge Mixtures¹

ABSTRACT

Batch experiments were undertaken to determine the effect of nitrilotriacetic acid (NTA) on the solubilities of Cu, Mn, Ni, Pb, and Zn in soil/sludge mixtures. Soil samples from Wye Coombe series (silt-loam, Rendolic Eutrochrepts) and Essex Windsor series (clay-loam, Haplaquepts) were each mixed with anaerobically digested sewage sludge and the influence of extraction time, NTA concentration, and pH on the solubility of NTA and metals was assessed. Removal of NTA from the liquid phase by soil/sludge colloids became constant after 8 h and was attributed to adsorption. The concentration of soluble Ni, Pb, and Zn increased in both soil/sludge mixtures with increases in NTA concentration from 0 to 0.212 mmol L^–1. Manganese was the least affected by the addition of NTA, and pH was shown to be the overriding influence on its solubility. In the Essex soil/sludge mixture, increasing the NTA concentration from 0 to 0.005 mmol L^–1 caused a sharp decrease in Cu solubility, with higher NTA concentrations having no further effect on soluble Cu levels. Addition of NTA did not significantly change Cu solubility in the Wye soil/sludge mixture. These results provide a basis to design further experiments to determine if increased heavy metal solubility could result if sludge containing NTA was applied to agricultural land.

Key Words: sludge disposal • adsorption • complexation • solubilization • detergent builder

¹ Contribution from the Public Health Engineering Laboratory, Dep. of Civil Engineering, Imperial College, London SW7 2BU, U.K.

² Research student, postdoctoral research assistant, lecturer and professor in the Dep. of Civil Engineering, Imperial College.

Received for publication December 21, 1983.