Effects of Biochar On Copper (Cu) Immobilization and Nutrient Release in Contaminated Soils.

Copper (Cu) is an essential micronutrient for plant and animal growth, but is toxic at excessive levels. By virtue of Jahn-Teller distortion and itself a d⁹ metal ion, Cu possess an extraordinary stability with oxygen- and nitrogen donor ligands. Biochar, a pyrolysis by-product of C-based biomass can potentially bind Cu, thus reducing its bioavailability. Laboratory incubation, column leaching, chemical characterization and chemical speciation study were conducted to assess the effect of biochar amendment on Cu immobilization and subsequent dissolved nutrient dynamics in Cu-contaminated Alfisol and Spodosol. The effects of dissolved C, N, P and K dynamics, other macronutrients such as Ca and Mg, and some trace metals concentration such as Zn, Fe, and Mn were assessed with biochar amendment. Biochar was found to be effective for Cu binding (30% and 41% for with-and without Cu-spiked Alfisol and the rate for the Spodosol were 36% and 43%, respectively) and mitigating Cu loss potential in leachates (47% reduced to10% for the Cu-spiked Alfisol and 48% reduced to 9% for the Cu-spiked Spodosol). For nutrients P, Ca, Mg, Zn, Mn, and NH₄-N were found to be significantly negatively (P<0.05) and K, Na, and NO₃-N were positively (P<0.05) correlated with biochar addition. Reduction of particulate-and dissolved-Cu and mitigation of nanoparticles concentration were also observed as a result of biochar incorporation. Biochar addition converted part of Cu from available pool to more stable forms. Decreased activity of Cu in free forms and increased activity in organic forms were observed. Results from this study documented the potential of biochar as an effective amendment for heavy metal immobilization and subsequently nutrient release in contaminated soils.