Effect Of Pisha Sandstone On Pollutants Adsorption And Transport Progress

Pisha sandstone(PS),widely distributed in the border region between Shanxi,Shaanxi and Inner Mongolia within Northwest China,induced severe erosion of water and soil in this area.As an inexpensive and easily obtained material,Pisha sandstone could be utilized as a resource to reduce its hazards and broaden its application.By far,the utilization of pisha sandstone had not reached the adsorption removal of aqueous phosphorus;the phosphorus adsorption capacity was proved to be poor and thus needed to be enhanced via modification on pisha sandstone.In this area,the potential threat to soil and underground water from extensively applied herbicides of nicosulfuron is not allowed to ignore.These two aspects could provide new way for pisha sandstone utilization and pollutants removal.This study aims to :(1)improve the P adsorprtion capacity of pisha sandstone via Al modification,determine the most economically appropriate modification ratio,investigate the P adsorption characateristics,influencing factors and adsorption mechanism;(2)investigate the effect of pisha sandstone addition ratios on the nicosulfuron adsorption characateristics,influencing factors and adsorption mechanism in aeolian sandy soil;(3)study the effect of pisha sandstone addition ratios on the breakthrough curves and transport model fitting parameters of chloride ion and nicosulfuron in aeolian sandy soil.The main conclusions were showed below:(1)As the Al modification ratio increased,the P adsorption capacities of Al-PS increased and the optimal Al-to-PS ratio was 0.81:1 theorectically.Comprehensively considering the modification cost and P removal efficiency,it was decided to apply 0.27:1 the Al-to-PS mass ratio in batch adsorption experiments and characterization.The adsorption kinetic and isothermal adsorption data could be well fitted by the pseudo-second-order and Temkin models,respectively.The Langmuir maximum P adsorption capacity was 4.21 mg/g,and the adsorption equilibrium was 24 h.At the initial pH of 7,with the increasing Al-PS dose,the P adsorption capacity showed a decrease while the removal rate showed an increase.The optimal pH for achieving the maximum adsorption capacity was 7.The P adsorption capacity of AlPS did not exhibit a clear response to changes in temperature.A possible adsorption mechanism was determined to be electrostatic adsorption.Al-PS could be a suitable clay adsorbent for P due to its low preparation temperature,simple modificatio procedure and low cost.After P adsorption,P-adsorded Al-PS might increase soil P content when it was applied in aeolian sandy soil and thus,a potential application of Al-PS could be as a eutrophication treatment agent that is subsequently used as a soil fertilizer(2)Of mixed aeolian sandy soil with three pisha sandstone mixing ratios(0%,30% and50%),the nicosulfuron adsorption kinetics and isothermal adsorption data could be well described by the pseudo-first-order model and linear model,respectively,which means the adsorption was due to nicosulfuron partition between water and soil.The nicosulfuron adsorption could be inhibited by the increasing pH.Organic matter content,pisha sandstone mixing ratios and nicosulfuron adsorption capacity were positively related mutually and significantly;the addition of pisha sandstone might raise the nicosulfuron adsorption capacity due to the increase of surface area,pore volume,pore sizes and other physical indicators as well as the partition of organic matters which was the possible adsorption mechanism of nicosulfuron.(3)The mixing of pisha sandstone in aeolian sandy soil could retard the transport of chloride ion and nicosulfuron in aeolian sandy soil and the retardation was enhanced with the increasing mixing ratios.Compared with CDE model,T-R model described the chloride ion breakthrough curves and the fitting parameters results suggested convection as the main transport approach of chloride ion in aeolian sandy soil mixed with pisha sandstone;T-S model described the nicosulfuron breakthrough better than CDE model did.The main reasons of the retardation in the transport of chloride ion and nicosulfuron in aeolian sandy soil by the addition of pisha sandstone were the reduce of average pore flow velocity inducded by pisha sandstone and the stronger adsorption of nicosulfuron by pisha sandstone than aeolian sandy soil.