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Colloid mobilization during soil iron redox oscillations

机译：土壤铁氧化还原振荡过程中的胶体动员

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In redox-dynamic soils, iron reduction-oxidation events may initiate wide shifts in the concentration of colloidal and dissolved material because of either Fe mineral dissolution or pH shifts associated with Fe oxidation state changes. This can have profound effects on the mobilization of organic and metal constituents. We conducted laboratory studies of colloid dynamics in a Hawaiian soil subjected to four consecutive 14-day reduction-oxidation cycles across the "soil-Fe" (Fe(OH)(3))/(Fe2+(aq)) equilibrium. Size fractionated samples were isolated by differential centrifugation and characterized based on analysis of the framework and trace elements (Si, C, Fe, Ti, Al, Zr, Nb, La, and U). Intracycle oscillations in all colloidal (3 kDa to 160 nm) elements peaked during the reduction half-cycles, mobilizing 10% of total soil Ti and from 1-5% of total soil Zr, Nb, La, and U at peak dispersion. Colloid dynamics were dependent on pH shifts accompanying the redox oscillations rather than the fluctuating solubility of Fe oxides. TEM/EDS and mass-balance calculations suggest a carbon-based colloid matrix with zones of metal enrichment. The cumulative effects of four redox cycles included an apparent increase in colloid stability. Proton production/consumption associated with Fe-redox cycling has important implications for mobilization colloid-borne trace elements and sorbed contaminants.
机译：在具有氧化还原作用的土壤中，由于铁矿物质的溶解或与铁的氧化态变化有关的pH值的变化，铁的还原-氧化过程可能引发胶体和溶解物质浓度的广泛变化。这会对有机和金属成分的动员产生深远影响。我们进行了夏威夷土壤中胶体动力学的实验室研究，该土壤经历了“土壤-Fe”（Fe（OH）（3））/（Fe2 +（aq））平衡的四个连续的14天还原-氧化循环。通过分级离心分离出大小分级的样品，并基于对骨架和微量元素（Si，C，Fe，Ti，Al，Zr，Nb，La和U）的分析进行表征。在还原半周期内，所有胶体（3 kDa至160 nm）元素的周期内振荡达到峰值，在峰值分散时动员了总土壤Ti的10％和总Zr，Nb，La和U的1-5％。胶体动力学取决于伴随氧化还原振荡的pH值变化，而不是Fe氧化物的溶解度波动。 TEM / EDS和质量平衡计算表明，碳基胶体基质具有金属富集区。四个氧化还原循环的累积作用包括胶体稳定性的明显增加。与铁-氧化还原循环相关的质子产生/消耗对胶体中的痕量元素和吸附的污染物的动员具有重要意义。

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