Potential of Biochar and Synthetic Iron Oxides for Chromium Immobilization in Tannery Waste Polluted Soil

The objective of this study was to determine Cr concentrations in tannery waste, surrounding soils and plants and to select possible amendments to immobilize Cr in the soil. Wastewater, soil and plant analyses were conducted for common quality parameters and heavy metals. A soil incubation experiment was conducted for 120 days using tea waste (5%), tea waste biochar (TWBC) pyrolyzed at 300°C (5%), synthesized Fe oxide (1%) and Zr-Fe oxide (1%). The Cr concentrations in tannery wastewater and soils ranged from 1 to 513 mg/L and from 800 to 19,000 mg/kg, respectively. Plants showed high concentrations. Cr was mainly bound to organic matter and carbonate fractions in the soil. TWBC reduced 90%, 50% and 40% of DTPA, CaCl_2, and EDTA extractable Cr, respectively. The distribution of exchangeable, carbonatebound, and Fe-Mn oxide-bound Cr decreased, whereas distribution of the organic matter bound fraction increased substantially with the above amendments. Iron oxide and Zr-Fe oxide showed only slight immobilization capacity for Cr in tannery waste contaminated soil. It can be concluded that TWBC can be a potentially effective low cost natural material to immobilize Cr.