Fractionation of lead-acid battery soil amended with Biochar

Abstract

Mobile (bio)available metal concentration in contaminated soils can be minimized through biological immobilization and stabilization methods using a range of organic compounds, such as “biochar.” Biochar has a high surface area, highly porous, variable – charge organic material that has the potential to increase soil water holding capacity, surface sorption and base saturation when added to soil. The soil was characterized before and after amending by standard method. The parent soil used for this study was collected from lead–acid battery chargers’ workshop. The physico-chemical properties of the soil are: pH=5.0, 0.24% organic carbon, 32.5 cmol.kg^-l CEC, 1.02, 23.0, 17.36, 10.05, 7.25 and 9.74 mg.kg^-l, for N, Na, P, Zn, Cu and Pb respectively. The pH, organic carbon and CEC of the biochar were 8.59, 78.70% and 82.27cmol.kg^-l respectively, while the concentration of heavy metals in the biochar ranged; 0.10 –1.20mg.kg^-l. There is a gradual decrease in the concentration of the heavy metals as the concentration of biochar increases from 5 – 20%. Fractionation result shows that the heavy metals (Zn,Cr,Cd,Cu and Pb) were mainly associated with the residual fraction, the mobility factor for the heavy metals was calculated and found to be higher for all metals in the parent soil than the Biochar amended soil. Contamination levels were moderate for Cd and Cr, considerably for Pb, Cu and Zn. The results indicated that long term discharge of these battery chargers’ wastes into the environment will cause accumulation of some toxic metals in soils which may lead to elevated levels of these metals in plants.

Keywords: Biochar, Lead–acid Battery, Fractionation and Heavy metals.