Research On Adsorption Mechanism Of Arsenic(?) In Groundwater By Cretaceous Red Sandstone In Hunan Province

In this paper,the common Cretaceous red sandstone in Hunan Province was selected as the adsorbent to study the adsorption of pentavalent arsenic ions.By studying the physical and chemical properties of red sandstone samples and combining with the existing forms of arsenic in red sandstones,it was found that natural red sandstone has certain adsorption potential for arsenic.By using the adsorption experiment system,Adsorption mechanism.The results of the study will promote the development of natural materials for the treatment of groundwater arsenic pollution and enrich the theories and techniques for the treatment of arsenic pollution in water bodies.It provides a reference for the treatment of groundwater arsenic pollution and has very strong practical significance.The paper mainly studied the physical and chemical properties such as mineral composition,chemical composition,specific surface area,zero charge and organic matter of red sandstone samples,adsorption and desorption characteristics of pentavalent arsenic in red sandstone samples,sandstone particle size,initial concentration of pentavalent arsenic,pH,temperature,reaction time and other factors on the adsorption reaction;arsenic in the red layer sample morphology;sandstone adsorption arsenic reaction kinetic characteristics;adsorption thermodynamic characteristics.The main findings are as follows:(1)The red sandstone physical and chemical properties analysis results show that:the red sandstone main minerals are quartz,calcite,mica,chlorite,feldspar,hematite,montmorillonite and so on.Sandstone samples of aluminum oxide,iron oxide,manganese oxide and other metal oxide content of 25.3%.Sandstone samples have a low organic matter content of 2.4 g/kg.The rock zero charge is 7.6.(2)The single-factor experimental results that the adsorption rate of arsenic to rock gradually decreases with the increase of initial concentration,and the adsorption rate increases with the decrease of particle size.In this experiment,The increase of temperature in the temperature range can promote the adsorption rate of arsenic in sandstone.When the environmental pH of the solution is lower than that of rock pHpzc,the adsorption of arsenic is better,and the adsorption efficiency becomes worse when the pH is higher.With the reaction time prolonging,Declining,and falling more slowly.(3)The simulation results of the kinetic model on the experimental data show that the second order model has the best fitting effect.The second order model shows a high similarity between the adsorption rate and the experimental process.This indicates that the adsorption of arsenic on red sandstone is mainly chemical adsorption.According to the change of adsorption rate,the adsorption process can be divided into three stages,and there are two or more than two rate factors in the adsorption process.(4)The results of thermostatic adsorption experiment show that the rock absorbs the heat during the adsorption of arsenic.By comparison,the Langmuir model fitted well to the isothermal adsorption process,and the adsorption reaction was a chemisorption mixed adsorption process.The thermodynamic analysis shows that the adsorption reaction spontaneously proceeds at an experimental set temperature and it is an endothermic reaction,and there is a physical adsorption reaction in this adsorption reaction.It shows that the arsenic desorption is accompanied by arsenic adsorption by arsenic or the arsenate is adsorbed in the rock before it enters the adsorption site or the entropy increase due to the substitution of adsorbed water molecules.So that the entropy change in this adsorption reaction there is a result of positive and negative.(5)According to the five-step extraction method,the order of the amount of various forms of arsenic adsorbed by a red layer was as follows:residue state>Fe-Mn oxide bound state>organic bound state>exchangeable state>carbonate bound state.The residue state and iron-manganese oxide accounted for 63.5%of the total,indicating that minerals in the red sandstone and iron-manganese oxide play a dominant role in adsorbing arsenic ions.