Influences Of Nitrate On Cr(Ⅵ) Removal By PRB From Groundwater

The production of chromate in our country is mass, groundwater will be pollutedby chromium slag after rain leaching into it. In addition, tanning, textile production,printing and dyeing, pigment and chromium plating chromium waste water fromfactories are major sources of chromium pollution in groundwater. Due to the high Cr(Ⅵ) toxicity and easy migration, once into the groundwater can cause serious threat tothe groundwater quality.As a groundwater repair technology,PRB is feasibilable andeffective. With the characteristics of cheap and high reduction potential and fastresponse,scrap iron has become one of the most effective response dielectricmaterials in recent years. But other pollutants existing in groundwater, such as nitratecan affect the removal of chromium by PRB, therefore， this study uses waste PRB torepair the polluted water of hexavalent chromium and focus on the influences ofnitrate.In this paper, removal efficiency of chromium and nitrate by scrap iron wasstudied,as well as the effect and main influence factors of Cr(Ⅵ) reduction by scrapiron in the presence of nitrate.Dynamic model of Cr(Ⅵ) reduction by scrap iron wasestablished.The results showed that;in the condition of chromium alone,the optimumdosage of scrap iron was15g/L and the best pH value was1.The reaction temperaturehad little effect on chromium removal by iron.At room temperature,chromiumrevomal efficiency is good by scrap iron, scrap iron can remove nitrate in groundwater,but the effect is not ideal.Static experiments by respectively studied the coexistence ofnitrate60,80,100mg/L and chromium5mg/L, research shows that: in the presence ofnitrate, chromium iron in addition to the optimal dosing quantity is10g/L, comparedwith chromium exists alone, found that different concentrations of nitrate can improvethe efficiency of chromium iron in addition to, but no specific linearrelationship;while60,80,100mg/L of nitrate and chromium coexist at pH1,3,5,7and9, with iron dosage of10g/L, the chromium removal rate can almost reach100%;while chromium exists alone, the removal rate can almost reach100%only at pH1 and3; through dynamic experiments simulating groundwater environment, in theearly stage of the reaction, different concentrations of chromium nitrate mixed withchromium can promote the reaction; when chromium is about to reach equilibrium,chromium removal efficiency decreased in the reaction column containing nitratecompared to the reaction column containing only chromium, which is probably due tothat the nitrate accelerated the consumption of iron, and compete with chromium,resulting in decreased removal efficiency of chromium.