Abstract

Adsorption of heavy metals by metal oxides is an effective method that is using to reduce the effects of heavy metals in recent years. The aims of this research were to compare the effects of non-stabilized and Na-carboxymethylcellulose (Na-CMC)-stabilized hematite on the immobilization of nickel and to investigate the effects of these amendments on different chemical forms of this metal in soil. For this purpose, a factorial experiment was conducted using a completely randomized design. The experimental factors were types and dosages of adsorbents (two types of adsorbents including non-stabilized and Na-CMC-stabilized hematite in four levels, including 0, 0.25, 0.5 and 1%) and the levels of soil total Ni (25, 75, 125, 175 and 325 mg kg-1). The results showed that the application of adsorbents to the soil decreased the concentration of Ni extracted by DTPA (Ni-DTPA) and MgCl2 (Ni-MgCl2). The concentrations of Ni-DTPA and Ni-MgCl2 decreased as the amount of adsorbent amount increased from 0.25 to 0.5%, but they increased as the amount of adsorbent increased from 0.5 to 1%. The reduction concentration rate of Ni-DTPA by application of 0.25, 0.5 and 1% non-stabilized hematite were 11, 13.9 and 9.63%, and by Na-CMC-stabilized hematite were 23.7, 35.9 and 20.3%, respectively, as compared to the control treatment. The results also showed that there were significant differences between Ni-DTPA and Ni-MgCl2 concentration in the non-stabilized and Na-CMC-stabilized hematite treatments. The results of sequential extraction in treatment with 175 mg Ni kg-1 soil showed that the adsorbent application significantly reduced soluble + exchangeable, carbonate forms of Ni, and increased the form associated with iron and manganese oxides compared to the control treatment.