Functional polypropylene fibers sphere combined with citric acid for efficient remediation of heavily cadmium (Cd) contaminated soil based on adsorption and citric acid recycling

Excessive Cd(II) in the soil seriously threats human health and ecological security. It is a challenge to efficiently remove Cd(II) from heavily contaminated soil by sustainable approaches without destroying soil ecological vitality and physicochemical properties. Here, functional polypropylene (AA/ASA-f-PP) fibers sphere with non-clogging, easy separation, and high selectivity for Cd2+ was prepared. It was combined with 0.2 g/L citric acid solution to remove Cd(II) from contaminated soil. Soil remediation result showed that more than 91% acid-soluble Cd(II), 83% oxidizable Cd(II), and 88% reducible Cd(II) could be removed, most of the unremoved Cd(II) was residual Cd(II) with poor bioavailability. A small amount of citric acid could ensure the adequate release of acid-soluble, oxidizable, reducible Cd(II) from contaminated soil into its solution by complexation. This was attributed to AA/ASA-f-PP fibers sphere could quickly capture Cd2+ from citric acid - Cd complex. Meanwhile, citric acid returned to its original state which can re-form the complex with Cd2+ and prompt Cd(II) release from the soil. The separation of citric acid solution from remediated soil could be omitted due to only ‰0.8 citric acid was introduced into the soil and Cd2+ was finally adsorbed to AA/ASA-f-PP fiber spheres. The generation of wastewater, soil nutrient loss, and high agent consumption can be avoided to ensure the cleaner production of soil remediation. Plant assay showed good ecological vitality of remediated soil and its feasibility for plant cultivation. These results provide a new insight for the remediation of Cd(II) contaminated soil. The potential risks of Cd(II) could be reduced or even eliminated with negligible changes in soil composition and properties. This technology holds the promise of Pb(II), Cu(II), Zn(II), and other heavy metals removal from contaminated soil within a few hours.