Immobilization and sorption of Cd and Pb in contaminated stagnic anthrosols as amended with biochar and manure combined with inorganic additives

The present study evaluated the efficiency of pre-selected composite amendments (CA-1: biochar-lime-sepiolite-zeolite and CA-2: manure-lime-sepiolite) for immobilization and sorption of Cd and Pb in field and batch sorption experiments. The field experiment was performed in a co-contaminated clay purple soil (stagnic anthrosols). Along with a control experiment (T1), CA-1 and CA-2 were tested at different rates including 750, 1500, 3000 and 6000 kg ha⁻¹ by growing wheat as the test crop. The obtained results revealed that the highest dose of both composites (T5: 6000 kg ha⁻¹ and T9: 6000 kg ha⁻¹) increased the soil pH to 6.85 and 6.81, respectively as compared to the control (5.63). DTPA-extractable Cd and Pb contents decreased with composite treatments (T7 and T4) at harvest stage samples. Metal fractionation depicted that application of amendments decreased the exchangeable fraction at harvesting stage. Application of CA-2 and CA-1 (3000 kg ha⁻¹) significantly increased the plant biomass (by 28% and 24%, respectively) and grain yield (by 26% and 22%, respectively) of wheat. Furthermore, batch sorption experiment results revealed that Langmuir adsorption model better fitted the sorption results with R² values ranging between 0.99 and 0.91 for Cd and Pb, respectively. CA-1 and CA-2 exhibited the maximum adsorption capacity for Cd with no significant difference among treatments but Pb adsorption capacity was highest in CA-1 followed by CA-2 and control. The results of our experiments revealed that the application of organics combined with inorganic materials enhanced Cd and Pb immobilization and sorption, consequently reducing metals availability in laboratory and field conditions. Moreover, for field trials, application of the composite amendments at 3000 kg ha⁻¹ emerged as the suitable treatment for tested wheat-grown area.