Effect Of Sulfur On The Species Of Fe, Mn, Cd And As Under Redox Condition In Paddy Soil

Redox conditions of the polluted paddy soil with exogenous As and Cdwere simulated by redox reaction apparatus after flowing N2and O2applied with differentforms of inorganic sulfur（CK-S0， elemental sulfur-S1and sulfate-S2） to study the effectof sulphur on species of Fe/Mn oxides and cadmium and arsenic in paddy soil. Resultsshowed that:1.Redox potential（Eh）was about-100--200mV and the pH7.0-8.0and the pe+pH4-7in soil solution when flowing N2， and Eh about200mV and the pH6.5-7.5and pe+pH9-12when continuously flowing O2.2. Amounts of soil Fe oxide by HCl extraction from different treatments were5g·kg-1lower than the original soil（21.4±0.3g·kg-1）when flowing N2， and it was in favor of thetransformation of crystal Fe2O3into amorphous iron and Fe2+. Activity of Fe oxides fromdifferent treatments increased comparing to that of the original soi（l46.8%）， and the orderof activity of Fe oxides was AsS2treatment（49.4%）<AsS1treatment（60%）. Fe2+insolution and FeS were oxidized into Fe3+， and hydrolysis of Fe3+was transformed into Fe（OH）3precipitation when flowing O2. It increased the contents of acid-soluble and crystalFe oxide， and the order of activity of Fe oxides was MS1（41.2%）treatment> MS2（36.1%）treatment.3. The activation of Mn oxides increased， it was higher under sulfate treatment thanunder elemental sulphur， that was: S2（76.8%）>S1（68.8%）， MS2（71.6%）>MS1（65.8%） and the content of amorphous manganese were higher than that of manganeseoxide in original soil as it is easy for crystal manganese oxide transferred to amorphousmanganese with N2flowing. While soil aging has begun and the content of crystalmanganese oxide increased and activation of Mn oxides oxide began to decrease by O2flowing.4. The proportions of arsenic fractions followed the order of the residual phases（34.9%-41.4%）≈specifically-sorbed（37.4%-39.5%）> well-crystallized hydrous oxides of Fe/Mn（23.3%-25.6%）> non-specifically sorbed（2.4%-3.3%）> amorphous hydrous oxides ofFe/Mn（0.5%-0.8%）when flowing N2， and of the residual phases（30.8%-39.3%）≈specifically-sorbed（30.3%-34.7%）> well-crystallized hydrous oxides of Fe/Mn（26.0%-28.7%）> amorphous hydrous oxides of Fe/Mn（9.3%-10.7%）> non-specifically sorbed（0.5%-1.6%）when flowing O2.Arsenic from amorphous hydrous oxides of Fe/Mn raised about9%by flowing O2than by flowing N2. This could be the effect of the agingamorphous Fe/Mn on the transformation of As.5No matter O2or N2flowed， the different fractions of cadmium ranked as followingorder: ion-exchange phases> Fe/Mn oxidized phase> carbonate bounded phase> weakorgnic phase> orgnic banded phase> residual phase. The contents of ion-exchange phaseand Fe/Mn oxidized phase was44.3%~49.8%，22.82%~25.23%，respectively when O2flowing.，while they changed into40.9%~42.7%，24.69%~33.49%when N2flowing.6The reducing condition could increase the activation of iron oxide and the mobility ofarsenic. The bioavailablity of cadmium was higher under reducing condition than oxidecondition. The sulfate system could decrease activation of iron oxide while it increased thatof manganese. The mobility of arsenic under elemental sulphur system was higher than thatunder sulfate system.7The proportions of sulphur fractions followed the order of the acid-soluble phasesS(33.8%~41.5%)> water-soluble phases S (22.2%-29.9%)> acid volatility phases S(11.7%~24.7%)>adsorbed phases S(16.5%~22.1%) when flowing N2, and of theacid-soluble phases S(28.2%~38.3%)> water-soluble phases S (19.4%-28.8%)≈acidvolatility phases S (20.3%~28.3%)>adsorbed phases S(14.4%~22.0%) when flowing O2,the proportions of the water-soluble phases S and acid-soluble phases S were higher whenflowing N2than flowing O2,while the proportions of the acid volatility phases S decreased.