DNNSA Reverse Micelle Extraction Purification Of Chromium-containing Wastewater

After entering the water body,the heavy metal wastewater will directly poison aquatic organisms and pollute the drinking water source.The damage is also irreversible.Moreover,Chinese chromium resources are relatively scarce,so the harmless treatment and recycling of chromium-containing wastewater is of great significance.Existing treatment technologies for heavy metal wastewater such as adsorption method and chemical precipitation method have the disadvantages of low treatment capacity and secondary pollution.Reverse micellar extraction belongs to microemulsion phase extraction,which still has the advantages of traditional extraction that is easy to achieve continuous operation,large processing capacity,and enrichment and recovery of heavy metals.In addition,the microemulsion phase extraction structure has variability and diversity,and can be adjusted and selected according to the target separation system,so it has good industrial application prospects.Dinonylnaphthalene sulfonic acid(DNNSA)is widely used in industry,with low raw material cost,and its critical micelle concentration(CMC)is on the order of 10^-5,usually in the form of reverse micelles.Therefore,in this paper,DNNSA reverse micelle extraction was used to purify Cr(?)-containing wastewater,and its extraction performance,extraction mechanism,extraction kinetics and back extraction were studied,and the following conclusions were obtained:(1)The extraction effects of DNNSA,P507,P204,TOA and TBP on Cr(?)were compared under three conditions of pH 0.24,3.77 and 8.01.It was found that only DNNSA maintained a good extraction effect on Cr(?)under three conditions.Taking Cr(?)as the extraction target of DNNSA reverse micelle,when the initial Cr(?)concentration was 3.85 mmol/L,the best research conditions are obtained.The enthalpy change in the extraction process?H⁽⁴⁸⁾was-9.20 k J/mol,the extraction reaction was exothermic.When the concentration of extractant DNNSA is 0.1 mol/L,the countercurrent extraction stage of Cr(?)of DNNSA reverse micelles by extraction isotherm is 4 stages.1 mol DNNSA extractant is combined with 0.05 mol Cr(?)ion,and the extraction capacity of DNNSA for Cr(?)is 4.88 mmol/L(253.76 mg/L).Using TEM and FT-IR to found that DNNSA formed intermolecular hydrogen bonds with H₂Cr O₄ and HCr O₄^-through their sulfonic acid groups(-SO₃H).(2)The kinetic mass transfer process of Cr(?)extraction by DNNSA reverse micelles was studied using a constant interface cell.In this extraction process,the extraction resistance zone is in the aqueous phase.When the stirring rate is 100-200r/min,the extraction rate increases with the increase of the stirring rate.At this time,the extraction reaction is controlled by diffusion.When the stirring rate is greater than 200 r/min,the extraction rate is no longer affected by the stirring rate.At this time,the extraction reaction process is controlled by both diffusion and chemical reactions.Moreover,the extraction rate of DNNSA reverse micelles to extract chromium ions is not affected by the area of the two-phase boundary.The extraction reaction is a type of chemical reaction kinetics control in the aqueous phase.Increasing the temperature is helpful to increase the extraction rate of DNNSA reverse micelles for chromium.The activation energy of the extraction process is 36k J/mol.Combined with the previous stirring rate affecting the experimental results,it is judged that the extraction process is controlled by both diffusion and chemical reactions.Through the isolated variable method of the initial chromium ion concentration and the extractant DNNSA concentration,the rate equation parameters are obtained;the relationship between the reaction rate constant and the temperature is obtained,and the rate equation is obtained.(3)When NaOH,NaCl,KCl,HNO₃,H₂SO₄ and HCl were used as stripping agents,it was found that NaOH had better stripping purification effect,and the stripping rate could reach 69%,and the conditions were optimized.The best stripping conditions are:when the concentration of Cr(?)supported by the extractant DNNSA is 1.81 mmol/L,the concentration of stripping agent NaOH is 0.1mol/L,which can reach the stripping equilibrium in 1 min,and the oil-water ratio is1:1.The enthalpy change of the NaOH back extraction purification load DNNSA process?H⁽⁴⁸⁾=-0.17 k J/mol,the reaction process is an exothermic reaction,and increasing the temperature is not conducive to the back extraction process.The stability of the extractant DNNSA was good.When the initial Cr(?)concentration of the water phase is 3.85 mmol/L,the extraction rate of Cr(?)can still reach more than 87%after nine cycles of use.