Effects of competitive adsorption with Ni(II) and Cu(II) on the adsorption of Cd(II) by modified biochar co-aged with acidic soil

To investigate the effects of competitive adsorption with Ni(II) and Cu(II) on the adsorption of Cd(II) by modified biochar co-aged with acidic soil, four biochars were employed in this study, namely original biochar, KMnO4modified biochar and two aged biochars which co-aged with an acidic soil using above biochars under freezethaw cycling and dry-wet cycling for 54 days simulating 6 years of natural aging. The results showed that biochar adsorption capacities of three heavy metal ions were in the order of Cd(II) > Cu(II) > Ni(II) in the single system while Cu(II) > Cd(II) > Ni(II) in binary and ternary systems. Modification improved biochar adsorption capacity of Cd(II), but competitive adsorption with Ni(II) and Cu(II) weakened the improvement of modification on adsorption performance of modified biochar in binary and ternary systems. The QMBC/QBC of Cd(II) (QMBC and QBC are the adsorption capacities of heavy metals by modified and original biochars) decreased from 231.57% (single system) to 216.67%-219.41% (binary system) and further decreased to 207.74% (ternary system). Coaging with soil weakened the adsorption capacities of biochars for Cd(II), even worse, competition aggravated this negative effect of co-aging. The QAMBC/QMBC of Cd(II) (QAMBC is the adsorption capacities of heavy metals by aged modified biochar) decreased from 65.41% (single system) to 14.43%-19.46% (binary and ternary systems). Therefore, the impact of competition should be fully considered when evaluating Cd long-term remediation effects of modified biochar in Cd polluted soils accompanied with other heavy metals.

Automated summary

This study investigated the effects of competitive adsorption with Ni(II) and Cu(II) on the adsorption of Cd(II) by modified biochar co-aged with acidic soil. The results showed that competitive adsorption weakened the improvement of modification on the adsorption performance of modified biochar. Co-aging with soil further decreased the adsorption capacities of biochars for Cd(II).