密度分离法提取土壤中微塑料的优化

Optimization of microplastics extraction from soil by density separation

为探究一种简单、经济和可靠的微塑料分离提取手段,设立了11种(F1~F11)具有不同体积比的饱和Na Cl和饱和Na I溶液的混合溶液,将混合液作为浮选液来提取土壤中的4种类型(聚乙烯,PE;聚苯乙烯,PS;聚氯乙烯,PVC;聚对苯二甲酸乙二醇酯,PET)微塑料,同时对浮选过程进行了改进.结果表明:当单独使用NaCl溶液浮选时,微塑料的总提取率为55.83%,但随着Na I所占体积比的不断增加,微塑料的总提取率基本呈上升趋势,在NaCl:NaI=1:1时总提取率超过了90%,在只有NaI的条件下总提取率高达96.67%;在F1~F11的任意条件下,PE和PS表现为较高的提取率,均超过了86.67%;PVC和PET在单独使用NaCl溶液浮选时提取率极低,在NaCl:NaI=1:1条件下提取率分别为93.33%和90%,接近单独使用Na I溶液浮选时的提取率;F1~F11任意条件下,低密度微塑料PE和PS的提取率之和均高于高密度微塑料PVC和PET的提取率之和,但在F6~F11条件下提取率差值不大.根据提取结果并结合经济成本等多方面因素考虑,建议使用NaCl:NaI=1:1的混合溶液来分离土壤中的微塑料.

To explore a simple,economic and reliable method for separation and extraction of microplastics from soil,eleven mixed solutions comprising saturated NaCl and NaI solutions with progressively changing volume ratios(F1~F11)were prepared.These mixed solutions were used as the flotation liquid to extract four types of microplastics including polyethylene(PE),polystyrene(PS),polyvinyl chloride(PVC),and polyethylene terephthalate(PET)absorbed by soil with an improved protocol for flotation separation.The results showed that the total extraction rate of microplastics was only 55.83%when used purely NaCl saturated solution,while this extraction rate increased with an growing volume ratio of NaI in the mixture.The total extraction rate exceeded 90%when the volume ratio of saturated NaCl solution to NaI solution was 1:1and reached as high as 96.67%when using purely NaI solution.For all the eleven mixed solutions used,the extraction rates of PE and PS exceeded 86.67%,relatively higher than that of the other two types of microplastics.When using saturated NaCl solution alone,the extraction rates of PVC and PET were extremely low compared with that of 93.33%and 90%respectively in case the volume ratio of NaCl to NaI solution was 1:1,which were close to those obtained using NaI solution alone.Sum of the extraction rates of lower-density microplastics PE and PS was constantly higher than that of higher-density microplastics PVC and PET for all the eleven mixed solutions.However,the difference between extraction rates was neglectable among the mixed solutions F6 to F11.Based on the abovementioned results and considering factors such as economic cost,it is recommended that the mixture of saturated NaCl to NaI solution with a volume ratio of of 1:1 could be the optimal to extract microplastics in soil samples.