背景离子类型和浓度对聚苯乙烯微塑料/铅在饱和石英砂中共运移的影响

为阐明水化学条件对微塑料和重金属运移的影响,初步明确两种环境污染物共运移过程中的耦合效应及其对环境条件的响应机制,研究了背景电解质离子不同价态和浓度组成条件下1μm聚苯乙烯微塑料(PS-MPs)和Pb²⁺在饱和一维砂柱中的单独及共迁移行为.结果表明:背景离子浓度的增加或价态的升高均会抑制PS-MPs的单独运移能力,当Na⁺浓度从1mmol/L增加到100mmol/L,PS-MPs和石英砂之间的排斥势垒下降了1348kT;当Ca²⁺浓度从1mmol/L增加到100mmol/L,PS-MPs和石英砂之间的排斥势垒下降了956kT.PS-MPs/Pb²⁺二元体系中Pb²⁺能降低PS-MPs的迁移能力,背景离子浓度和价态的提升可削弱Pb²⁺对PS-MPs运移能力的抑制性.当Na⁺浓度从1mmol/L增加到100mmol/L,PS-MPs和石英砂之间的排斥势垒下降了1100kT;当Ca²⁺浓度从1mmol/L增加到100mmol/L,PS-MPs和石英砂之间的排斥势垒下降了543kT.背景离子浓度的增加或价态的升高能促进Pb²⁺的单独运移能力.PS-MPs/Pb²⁺二元体系中,PS-MPs能够促进Pb²⁺的运移,背景离子浓度较低时,PS-MPs负载Pb²⁺的迁移率较高,反之亦然.对于PS-MPs和Pb²⁺单运移体系,背景阳离子浓度和价态的提升可进一步屏蔽PS-MPs及石英砂表面负电荷,竞争吸附石英砂表面结合位点,抑制PS-MPs运移,促进Pb²⁺运移;对于PS-MPs和Pb²⁺共运移体系,背景离子浓度和价态的提升可通过调节Pb²⁺与PS-MPs及石英砂表面的相互作用,削弱Pb²⁺对PS-MPs迁移能力的抑制作用.背景离子对PS-MPs表面位点的竞争吸附及对电荷的屏蔽效应影响PS-MPs对Pb²⁺的负载迁移能力.

Effects of background ion types and concentrations on the co-transport of polystyrene microplastics / lead in saturated quartz sand

In order to elucidate the effect of hydrochemical conditions on the transport of microplastics and heavy metals, and to clarify the coupling effect in the co-transport process of the two environmental pollutants and their response mechanism to environmental conditions preliminarily, the effects of background electrolyte ions with different valence and concentrations on the individual and co-transport behaviors of 1μm polystyrene microplastics (PS-MPs) and Pb²⁺ in a saturated one-dimensional sand column were studied. The experimental results showed that the increase in the background ion concentration or the valence would inhibit the individual transport ability of PS-MPs. When the Na⁺ concentration increased from 1mmol/L to 100mmol/L, the repulsive barrier between PS-MPs and quartz sand decreased by 1348kT; when the Ca²⁺ concentration increased from 1mmol/L to 100mmol/L, the repulsive barrier between PS-MPs and quartz sand decreased by 956kT. Pb²⁺ in PS-MPs/Pb²⁺ binary system could reduce the transport ability of PS-MPs, and the increase of the background ion concentration and the valence can weaken the inhibition of Pb²⁺ on the transport ability of PS-MPs. When the Na⁺ concentration increased from 1mmol/L to 100mmol/L, the repulsive barrier between PS-MPs and quartz sand decreased by 1100kT; when the Ca²⁺ concentration increased from 1mmol/L to 100mmol/L, the repulsive barrier between PS-MPs and quartz sand decreased by 543kT. The increase in the background ion concentration or the valence can promote the individual transport ability of Pb²⁺. PS-MPs can promote the transport of Pb²⁺ in the binary system of PS-MPs/Pb²⁺. When the background ion concentration was low, the transport of Pb²⁺loaded by PS-MPs was higher, and vice versa. For PS-MPs and Pb²⁺ individual transport systems, the increase in background cation concentration and valence can further shield the negative charges on the surface of PS-MPs and quartz sand, competitive adsorption the surface binding sites of quartz sand, inhibits the transport of PS-MPs while promoting Pb²⁺ transport. For the co-transport system of PS-MPs and Pb²⁺, the increase in background ion concentration and valence can weaken the inhibitory effect of Pb²⁺ on the transport ability of PS-MPs by adjusting the interaction between Pb²⁺ and PS-MPs and the surface of quartz sand. The competitive adsorption of background ions to PS-MPs’ surface sites and the shielding effect on charges affect the transport ability of Pb²⁺ loaded by PS-MPs.