Immobilization of heavy metals in soils using inorganic amendments in a greenhouse study

The effect of red mud (10 g kg(-1)), a by-product of the alumina industry, zeolite (20 g kg(-1)), a naturally-occurring hydrous aluminosilicate, and lime (3 g kg(-1)) on metal lability in soil and uptake by fescue (Festuca rubra L.) (FEST) and amaranthus (Amaranthus hybridus L.) (AMA) was investigated in four different soils from Austria. The soil collection locations were Untertiefenbach (UNT), Weyersdorf (WEY), Reisenberg (REI), and Arnoldstein (ARN). The latter was collected in the vicinity of a former Pb-Zn smelter and was highly polluted with Pb (12300 mg kg(-1)), Zn (2713 mg kg(-1)), and Cd (119.7 mg kg(-1)) by long-term deposition. The other soils were spiked with Zn (700 mg kg(-1)), Cu (250 mg kg(-1)), Ni (1100 mg kg(-1)), V (100 mg kg(-1)), and Cd (7 mg kg(-1)) salts in 1987. The two plant species were cultivated for 15 months. Ammonium nitrate (1 M) extraction was used in a soil : solution ratio of 1:2.5 to assess the influence of the amendments on the labile metal pools. The reduction of metal extractability due to red mud was 70 % (Cd), 89 % (Zn), and 74 % (Ni) in the sandy soil (WEY). Plant uptake in this treatment was reduced by 38 to 87 % (Cd), 50 to 81 % (Zn), and 66 to 87 % (Ni) when compared to the control. Sequential extraction revealed relative enrichments of Fe-oxide-associated metal fractions at the expense of exchangeable metal fractions. Red mud was the only amendment that decreased lability in soil and plant uptake of Zn, Cd, and Ni consistently. Possible drawbacks of red mud application (e.g., As and Cr concentration) remain to be evaluated.