Comparative immobilization of lead, cadmium, and copper in soil using dead bacterial biomass and graphitic carbon nitride nanomaterials

• Dead bacterial biomass and g-C₃N₄ were compared for immobilization of HM in soil. • BM is a cost-effective and environment-friendly adsorbent for remediation of soil. • The RS-fraction of metals was high at higher adsorbent dosage. • The immobilization efficiency of the heavy metals was highest for Cu. • Maximum RS fraction was obtained in the first three days of incubation. Heavy metals (HM) are known to pose severe harm to the soil, crops, and human beings. The usefulness and efficiency of metal immobilization of Pb, Cd, and Cu ions using different doses of dead bacterial biomass (BM) and graphitic carbon nitride (g-C 3 N 4 ) was evaluated and compared in spiked soil. The effectiveness of BM and g-C 3 N 4 to immobilize metals in soil depends on the metal characteristics, dose of adsorbent, and contact time. The soil was spiked with two different metal concentrations. When comparing the two adsorbents, there was no significant difference observed in the immobilization of metals. Results showed a significant relationship between BM, g-C 3 N 4, and metal fractions. At 200 mg kg -1 BM, the increase in the RS fraction (residual fraction) of Pb, Cd, and Cu was 42, 44, and 68 %, respectively. At 200 mg kg -1 g-C 3 N 4, the RS fraction of Pb, Cd, and Cu was 48, 43, and 83 %, respectively. The maximum reduction in the exchangeable metal fraction was observed during the first 3 days of incubation. The adsorption of metals increased with time. Cu showed the highest adsorption (57 %) followed by Cd and Pb. The Cd adsorption increased from 35 % at Cd_125 to ∼55 % at Cd_275. There was no noticeable variation in the adsorption of Cu and relatively higher adsorption (35 %) was observed at Pb_160 and dropped to 30 % at Pb_330. The present study suggests using dead bacterial biomass as a cost-effective and environmentally benign adsorbent for the remediation of HM-contaminated soils instead of chemically synthesized nanomaterials.