Study On Adsorption Of Zn²⁺ By Triclinic Birnessite And Its Reaction Mechanism

Zinc as one of heavy metals in industrial wastewater is harmful to human health.Mineral method is very effective to adsorb and purify heavy metals in wastewater because of its wide sources in nature,low costs,and no secondary pollution.Birnessite is the most common layer manganese oxide mineral in nature,and has the the biggest adsorption capacity for heavy metal ions among manganese oxides minerals.There are triclinic and hexagonal birnessite in nature,and the researchers was focus on the study of hexagonal birnessite(H-birnessite,referred to as H-birn),rather than triclinic birnessite,which results in the geochemical behavior of triclinic birnessite(Na-birnessite,referred to as Na-birn)in soil/water is not still clear.Therefore,synthysized Na-birn is used as material to react with Zn2+in order to study the adsorption effect and its mechanism in this paper.In order to explore the influence of different reaction time,different pH,and different content of Na-birn to Zn2+adsorption.At 25℃,150 r/min,initial concentration of Zn2+is 163.90 mg/L,20 ml,carry out series experiments and the results show that:Na-birn adsorbs more Zn2+as time goes and with the increase of Na-birn,but Na-birn adsorbs less Zn2+ as pH increases.We get the best experimental conditions of single factor:pH=3,the content of Na-birn is 0.12 g and react 6 h,the concentration of Zn2+is 0.09 mg/L,the concentration of Mn2+is 0.36 mg/L and pH is 6.35 after reaction,all achieve the primary standard of national sewage comprehensive discharge and there is no secondary pollution.Compare the Zn2+adsorption effect between Na-birn and H-birn.Under the condition of pH=3.03,other conditions are same(initial concentration of Zn2+is 163.90 mg/L),the concentration of Zn2+is 4.10 mg/L and the adsorption rate is 97.50%after the reaction of Na-birn with Zn2+,the concentration of Zn2+is 142.25 mg/L and the adsorption rate is 13.21%after the reaction of H-birn with Zn2+,the adsorption effect of Na-birn is much better than that of H-birn.Explore the adsorption mechanism of Zn2+and Na-birn by XRD,SEM+EDS,XPS and ICP-AES.Drawn the following conclusions:At pH=3.00-4.03,Na-birn transforms to H-birn,consuming H+and creating vacant due to the disproportionation reaction of Mn3+,which make Zn2+enter into the interlayer of H-birn and adsorb above and below the vacant by special adsorption,or Zn2+may adsorb on the surface of minerals by physical adsorption.From what has been discussed above,under the appropriate condition,Na-birn has good adsorption effect on 2n2+,solution conform to the primary standard of national sewage comprehensive discharge after the reaction and there is no secondary pollution.Zn2+ may be in the structure of mineral in the form of special adsorption or on the surface of mineral in the form of physical adsorption.It provides basic theory basis for purification treatment of heavy metal ions in soil/water by Na-birn.