Selenium adsorption by New Zealand soils

Abstract

Abstract Samples of 66 representative New Zealand surface soils were equilibrated with 0.01 M Na 2 SeO 3 solution fo measure their relative adsorption of Se as selenite ions. Nineteen other soil properties were determined and the observed Se adsorption was related to them. Amounts of Se adsorbed tanged from 39 to 3356 mg Se/kg soil and averaged 1621 mg Se/kg soil. This represented removal of 1–85% of added Se (average 41 %). Among soils from noncalcareous sedimentary and metamorphic rocks, adsorption increased as weathering increased, from brown‐grey earths through to northern yellpW‐brown earths, except that podzols adsorbed the least Se. Compared with soils from sed,imentary and metamorphic parent material, yellow‐brown pumice soils developed on rhyolitic volcanic ash adsorbed medium amounts of Se, and yellow‐brown loams, red and brown loams, and brown granular clays developed on rhyolitic, andesitic, and basaltic materials adsorbed greater amounts. Amounts of Se adsorbed were closely related to specific surface area, organic C, “free” forms of SiO 2 , Al 2 O 3 , and Fe 2 O 3 , and “allophane” content. Adsorption increased as the ratio between NaOH‐extractable SiO 2 and Al 2 O 3 approached that of “allophane” composition. Both amorphous and crystalline forms of Fe 2 O 3 and SiO 2 were related to Se adsorption. Multiple regression on dithionite‐Fe 2 O 3 , Tamm's‐Fe 2 O 3 , organic C, Tamm's‐SiO 2 , and the M SiO 2 / M Al 2 O 3 ratio and SiO 2 content from hot NaOH extraction accounted for 91.8% of variance in Se adsorption.