High decrease in soil metal bioavailability by metal immobilization with halloysite clay

Increasing pollution by heavy metals calls for advanced methods to immobilize or extract soil metals, thus avoiding their contact with water, air and living organisms. In particular there is a need for cheap binding materials that extract metals. Here we tested the use of the halloysite clay, functionalized with silanes and non-functionalized, on metal extraction from soils. The clay was functionalized with 3-mercaptopropyl-trimethoxysilane and 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane. Contaminated soils were sampled at the Glogow Copper Smelter and Refinery. Soils were sequentially extracted using the Tessier method. Metals were quantified by atomic absorption spectroscopy. Our results show that the addition of halloysite increases the metal content of the plant unavailable fraction that is the fifth fraction of the Tessier method, thus decreasing metal availability. Indeed metal contents of the fifth fraction versus total content increased from 67.64 to 157.79 mg/kg for copper, from 28.10 to 76.14 mg/kg for lead, from 41.60 to 95.78 mg/kg for zinc, from 0.77 to 1.79 mg/kg for cadmium and from 3.96 to 8.90 mg/kg for arsenic.