A novel technique for Cd removal from soil based on alginate-derived floatable spheres

The novel technique for activation-removal Cd from soil via two types of floatable alginate-derived multifunctional spheres: magnetic hollow carbon composite (MHCC) and calcium alginate aerogel (CAA) spheres. [Display omitted] •Activate and adsorb Cd from soil through two floatable spheres (MHCC and CAA)•5-round successive treatments by MHCC-CAA, about 44.02% of soil anchored Cd is removed.•The eco-friendly MHCC-CAA spheres can be easily collected and recovered. This paper proposes a fast, facile and eco-friendly strategy for removing Cd from soil. By combining two types of floatable alginate-derived multifunctional spheres: magnetic hollow carbon composite (MHCC) and calcium alginate aerogel (CAA) spheres, the fixed state Cd in soil is activated and removed sequentially. MHCC spheres activate and desorb the solid phase anchored Cd into mobile Cd2+ ions, and CAA spheres effectively absorb the free Cd2+ ions from the liquid phase via the massive absorption sites of carboxy and hydroxy groups. The remediation results of 5-round successive MHCC-CAA treatments (1.5 g MHCC-0.45 g CAA in 60 g soil) show that 44.02% of Cd is removed from the soil. MHCC spheres demonstrate excellent recyclability of 88.87 and 94.45% in flooding and non-flooding soil, respectively. The texture, cation exchange capacity (CEC) and pH value of the remediated soil suggest that the MHCC-CAA system has little interference on the soil properties. No remarkable hindrance of microbial growth by MHCC or CAA spheres is observed in the eco-toxicological test, indicating the ecological friendliness of MHCC-CAA remediation system.