重金属污染农田修复植物龙葵与伴矿景天的生物质处置技术

Safe disposal technologies of post-harvest Cd-rich hyperaccumulator Solanumnigrum L. and Sedum plumbizincicola in heavy metal contaminated farmland

植物修复是重金属污染农田的一种环保型治理技术,但植物修复技术产生了一个新的难题——大量含重金属的生物质。为快速处置含镉超富集植物生物质,采用不同提取剂对产后龙葵和伴矿景天生物质中的镉(cadmium,Cd)进行液相萃取,并对其萃取废液通过物理(4Å分子筛)和化学(KOH和K_(2)CO_(3))方法进行了处理。分别考察了不同提取剂种类、浓度对修复植物生物质中重金属镉萃取效果的影响,探讨了重金属废水不同处理措施对萃取废液中镉的去除效果。结果表明,0.25 mol∙L^(−1)盐酸(HCl)、0.25 mol∙L^(−1)硝酸(HNO3)、0.25 mol∙L^(−1)硫酸(H_(2)SO_(4))和0.10 mol∙L^(−1)乙二胺四乙酸二钠(disodium ethylenediaminetetraacetate,EDTA)4种提取剂对龙葵茎和叶中Cd的萃取效果最佳,且茎和叶中Cd的萃取率最高分别达88.2%和89.8%;4种提取剂的Cd萃取率之间无显著性差异(P>0.05)。不同提取剂对伴矿景天生物质中Cd的萃取率均在50%以下,表现为0.25 mol∙L^(−1)盐酸≈0.25 mol∙L^(−1)硝酸≈0.25 mol∙L^(−1)硫酸>0.10 mol∙L^(−1)乙二胺四乙酸二钠。4Å分子筛对萃取废液中Cd的后续净化效果最佳,在处理高浓度Cd后,萃取液中最终Cd质量浓度达到0.10 mg∙L^(−1)的污水排放标准(GB 8978-1996)。综合考虑提取剂萃取修复植物中Cd的效率、提取剂的成本与后续萃取废液中Cd的去除效果,0.25 mol∙L^(−1)盐酸作为液相萃取的提取剂最合适,4Å分子筛作为萃取废液的净化剂最为高效。

Phytoremediation is an environment friendly technique for heavy metal contaminated farmland.However,the technique will produce large amounts of biomass as hyperaccumulator residues.For a rapid safe disposal of Cd-rich hyperaccumulators,different extractants were tested for Cd liquid extraction from the aboveground biomass of Solanum nigrum L.and Sedum plumbizincicola.Physical(4Å molecular sieve)and chemical(KOH and K_(2)CO_(3))methods were used to remove Cd in the extracted liquids to meet the requirements of sewage discharge standard.Effects of different extractants and extractant concentrations on Cd extraction in the plant biomass were investigated,and performance of different heavy metal wastewater treatment methods on Cd elimination in extracted liquids were compared.The results showed that 0.25 mol∙L^(−1) hydrochloric acid(HCl),0.25 mol∙L^(−1) nitric acid(HNO_(3)),0.25 mol∙L^(−1) sulfuric acid(H_(2)SO_(4)),and 0.10 mol∙L^(−1) disodium ethylenediaminetetraacetate(EDTA)showed the optimum extraction efficiency of Cd from the stems and leaves of Solanum nigrum L.,and the corresponding highest Cd extraction rates were 88.2%and 89.8%from the stems and leaves of Solanum nigrum L.,respectively.There were no significant differences between these different extractants(P>0.05).The Cd extraction efficiencies by different extractants from the shoots of Sedum plumbizincicola were less than 50%,with the order of 0.25 mol∙L^(−1) HCl≈0.25 mol∙L^(−1) HNO_(3)≈0.25 mol∙L^(−1) H_(2)SO_(4)>0.10 mol∙L^(−1) EDTA.The 4Å molecular sieve was the most effective material for the subsequent elimination of Cd in extracted liquids,and the final Cd concentration in liquids was lower than 0.10 mg∙L^(−1) and met the effluent discharge standard(GB 8978-1996,0.10 mg·L^(−1))in China.Given the extraction efficiency of Cd,the cost of the extractant,and the subsequent elimination of Cd from the extracted liquid,0.25 mol∙L^(−1) HCl and 4Å molecular sieve were the best alternatives of the extractant of the liquid extraction and the agent of Cd removal from the extracted liquid for post-harvest treatment of hyperaccumulator.