Application Of Sponge Iron And Bio-ferric Sludge In Treating Cr(?)-contaminated Water And Remediation Of Cr(?)-contaminated Soil

Because of the Cr(?)waste water and waste slag produced in industrial production by human beings,cause the Cr(?)content in water bodies and soils exceed standards,which destroys the natural environment and effects hunman health.Therefore,it is imperative to solve Cr(?)pollution in water bodies and soils.Sponge iron and bio-ferric sludge materials,which have both reducing and adsorbing properties,have achieved fruitful research results in some water treatment industries,bio-ferric sludge materials is sponge iron added to ordinary activated sludge.Under the joint action of biological and iron,it can strengthen adsorption,coagulation,biodegradation and sedimentation.but there are few reports on the treatment of Cr(?)pollution.In this paper,the effects of sponge iron on the removal of Cr(?)in water and soil were studied.The optimal removal conditions were discussed using response surface method.The effects of sponge iron in soil column leaching experiments and the reduction mechanism of Cr(?)on sponge iron were described.Through experiments,the results are as follows:(1)Single factor experiments show that,for Cr(?)in water,sponge iron shows a high removal rate under different control conditions.Sponge iron and bio-ferric sludge are more suitable for removing Cr(?)under the condition of pH = 2 in Cr(?)solution;the highest removal effect is achieved when the dosage of sponge iron is 5g /L,and the best of bio-ferric sludge.The dosage is 2g / L,which is less than sponge iron;sponge iron reaches equilibrium after 30 minutes of reaction,and bio-ferric sludge only takes 15 minutes.(2)Based on response surface experiments of sponge iron to remove hexavalent chromium in water,under the experimental operating conditions,the optimized conditions are respectively at pH = 2.01,sponge iron dosage is 2.93 g,and initial concentration is 51.65 mg / L.The adsorption rate of Cr(?)was 100%.It was verified in accordance with the optimal adsorption conditions.Repeated three times,the removal rate of Cr(?)was 99.3%.According to the response surface experiments of Cr(?)removal from water by bio-ferric sludge,under the experimental operating conditions,the optimized conditions were pH = 1.73,the dosage of bio-ferric sludge was 8.53 g,and the initial concentration of Cr was 32.67 mg / L.Cr(?)Removal is 100%,and the verification is performed according to the optimal adsorption conditions.Repeated three times,the Cr(?)removal rate is 99.0%.(3)The kinetic study of Cr(?)removal from sponge iron by the sponge iron shows that the adsorption process is more in line with pseudo-second-order kinetics.Through adsorption isotherm research,it was found that the adsorption of Cr(?)in water by sponge iron is more in line with Freundlich isotherm and n> 1.The thermodynamic study shows that the adsorption of Cr(?)by sponge iron is an endothermic reaction,? G <0,which indicates that the reaction is spontaneous.The kinetic study of Cr(?)removal in water from bio-ferric sludge shows that the adsorption process is more in line with pseudo-second-order kinetics.According to the adsorption isotherm research,it was found that the removal of Cr(?)in water by bio-ferric sludge was more in line with the Langmuir isotherm adsorption model,and the adsorption amount reached 3.66 mg / g.The thermodynamic study shows that the adsorption of Cr(?)by sponge iron is an endothermic reaction,? G <0,which indicates that the reaction is spontaneous.(4)The single factor experiment shows that for different Cr(?)in soil,sponge iron shows a higher removal rate under different control conditions.Sponge iron and bio-ferric sludge are more suitable for removing Cr(?)under the condition of pH = 2in Cr(?)soil;the highest removal effect is achieved when the dosage of sponge iron and bio-ferric sludge is 3g / 20g;sponge.The optimal reaction time of iron and bio-ferric sludge is 10 minutes after reaching equilibrium.Although the level of influencing factors is the same,sponge iron exhibits a higher removal effect under the same influencing factors.Moreover,unlike the removal of Cr(?)in aqueous solution,the soil needs a certain amount of water content to have a good removal effect,whether it is sponge iron or bio-ferric sludge,only when the soil water content is more than 12 ml,have a better removal effect.(5)According to the response surface experiments of sponge iron to remove hexavalent chromium in water,under the experimental operating conditions,the optimized conditions were respectively at a pH of 1.14 and the initial Cr(?)contaminated soil content was 28.29 mg / kg.When the amount is 4.06 g,the removal effect is the best,which can reach 100%.After verification experiments,the removal effect can reach 98.9%.According to the response surface experiment of removing hexavalent chromium from water by bio-ferric sludge,under the experimental operating conditions,the optimized conditions were: pH 1.56,initial Cr(?)contaminated soil content was20.89 mg / kg,sponge iron was added.When the amount is 3.89 g,the removal effect is the best,which can reach 100%.After verification experiments,the removal effect can reach 98.0%.(6)The kinetic study of hexavalent chromium removal from sponge iron by sponge iron shows that the adsorption process is more in line with pseudo-second-order kinetics.Through adsorption isotherm research,it was found that the adsorption of Cr(?)in water by sponge iron is more consistent with Langmuir.Through thermodynamic research,Gibbs free energy?G of sponge iron's Cr(?)adsorption process at temperatures of 283.15 K and 293.15 K,and sponge iron's Cr(?)adsorption.The Gibbs free energy?G <0 of the process.The kinetic study of Cr(?)removal in water from bio-ferric sludge shows that the adsorption process is more in line with pseudo-second-order kinetics.Through adsorption isotherm research,it was found that the removal of Cr(?)from water by biological iron bio-ferric sludge is more consistent with the Langmuir isotherm adsorption model.Based on thermodynamic studies,the Gibbs free energy ?G of the adsorption process of Cr(?)by sponge iron at 283.15 K and 293.15 K is greater than0.Gibbs free energy ?G <0.(7)According to the previous data,it is known that sponge iron is suitable for the reaction under acidic conditions of pH = 2 in both water and soil.Under the optimal reaction conditions,sponge iron is suitable for Cr(?)in water.The removal amount is higher than Cr(?)in the soil,and the reaction in the soil requires a certain water content to be carried out.The water content required in the experiment is ?12ml.For bio-ferric sludge,it is more suitable to achieve the best removal rate under acidic conditions in both water and soil.The removal of Cr(?)from soil by bio-ferric sludge is slightly higher than that of water.The reaction in the soil requires a certain amount of water content to be carried out.The required water content in the experiment is ?12ml.(8)Based on experiments on the reduction performance of Cr(VI),the possible Cr(VI)reduction reaction process was analyzed: Cr(VI)was first adsorbed to the surface of sponge iron by adsorption,and some Cr(VI)was absorbed by sponge iron.Fe0-containing electrons provide electron reduction to Cr(III).Part of the generated Cr(III)continued to be adsorbed on the surface by sponge iron,while the remaining part was freed in solution.(9)Soil column leaching experiments show that when using leachate with pH = 2,a soil column with a sponge iron dosing amount of 15% is best for Cr(?)treatment.The greater the amount of eluent,the better the eluent effect,and the best eluent effect at 800 ml.