Preparation Of Polypropylene-based Selective Adsorption Fibers-ball And Its Application In Heavy Metal Contaminated Soil Remediation

Soils contamination caused by heavy metals,such as Cd(Ⅱ),Pb(Ⅱ),and Cu(Ⅱ)threats directly or indirectly ecosystem security and human health,how to efficiently remove heavy metals from contaminated soil while ensuring soil physicochemical properties and ecological vitality is a worldwide problem.The separation and extraction of heavy metals from contaminated soil undoubtedly is one of the most effective technologies for the remediation of heavy metals contaminated soil.Two challenges need to be solved to achieve this objection while avoiding damage to the properties and composition of the soil as much as possible:at first,heavy metals could be released from contaminated soil;at second,heavy metals ions released can be separated.In this paper,functionalized polypropylene fibers-ball with complexing groups was employed to rapidly and selectively adsorb heavy metals ions from soil-water system,combining adding a small amount of citric acid prompted the release of Cd(Ⅱ),Pb(Ⅱ),Cu(Ⅱ)from contaminated soil,based on the dynamic equilibrium of heavy metals ions rapid release-selective adsorption,a rapid migration route of heavy metals from soil→water or dilute citric acid solution→functionalized polypropylene fibers-ball was established,and the remediation of Cd(Ⅱ),Pb(Ⅱ)and Cu(Ⅱ)contaminated soil can be achieved.The structure and function of functionalized polypropylene fibers-ball is the key to“release-adsorption synergy mechanism”in this paper.Using polypropylene fibers as the matrix made the density of fibers-ball is slightly less than that of water,which can not only ensure that most of the fibers-ball is immersed in water to facilitate adsorption,but also floats on the water surface to facilitate separation;Functionalized fibers possessed a larger specific surface area,which could ensure the rapid adsorption of fibers-ball;The types and combinations of functional groups on the surface of fibers provided the selective adsorption and competitive adsorption capacity of functionalized polypropylene fibers-ball for different heavy metals ions in complex multi-ionic system;The functionalized polypropylene fibers-ball was composed of tens of thousands of flexible fibers radially,and the density gradually decreased from the inside to the outside,which ensured that the fibers-ball cannot be blocked by soil particles when it is used in soil-water system;The diameter regulation of the functionalized polypropylene fibers-ball can improve its adsorption capacity of heavy metal ions in soil-water system,reduce separation difficulty;The efficient removal of heavy metals from contaminated soil can be achieved and the cost of soil remediation can be reduced by controlling the dosage of functionalized polypropylene fibers-ball.Acrylic acid(AA)was introduced onto the surface of polypropylene fibers(PP)by UV radiation grafting to obtain carboxyl functionalized polypropylene fibers(PP-g-AA)with 47.8%grafting degree of AA,and then PP-g-AA fibers were assembled into fibers-ball with density of 0.967 g/cm~3 and diameter of about 1 cm by ligature,shearing.Combining PP-g-AA fibers-ball with water,more than 90%acid-soluble Cd(Ⅱ)can be removed from contaminated soil within 12 h and the ecological risk of Cd(Ⅱ)in the soil can be migrated.PP-g-AA fibers-ball possessed excellent stability and reusability during the remediation of Cd(Ⅱ)contaminated soil.5-aminosalicylic acid(5-ASA)was introduced onto the surface of PP-g-AA fibers by amidation reaction to obtain carboxyl,amide and hydroxyl functionalized polypropylene fibers(PP-g-AA-ASA)with 5-ASA content of 1.52 mmol/g,and PP-g-AA-ASA fibers were then assembled into fibers-ball with density of 0.971 g/cm~3and diameter of about 1 cm.Combining PP-g-AA-ASA fibers-ball with 0.2 g/L citric acid solution,more than 90%acid-soluble Cd(Ⅱ),more than 85%oxidizable and reducible Cd(Ⅱ)can be removed from contaminated soil,and remediated soils showed good ecological vitality.L-cysteine(L-Cys)was introduced onto the surface of PP-g-AA fibers by amidation reaction and redox reaction to obtain carboxyl,amide and sulfhydryl functionalized polypropylene fibers(PP-g-AA-Cys)with L-Cys content of 2.16mmol/g,PP-g-AA-Cys fibers were then assembled into fibers-ball with density of 0.975g/cm~3and diameter of about 1 cm.Combining PP-g-AA-Cys fibers-ball with 0.2 g/L citric acid solution,more than 70%Pb(Ⅱ),more than 65%Cu(Ⅱ)can be removed from contaminated soil,and the contents of Pb(Ⅱ),Cu(Ⅱ)in remediated soil were lower than the screening values of soil contamination in agricultural land(GB15618-2018).PP-g-AA-Cys fibers-ball possessed excellent stability and reusability during the remediation of Pb(Ⅱ),Cu(Ⅱ)contaminated soil.