Adsorption Of Cu²⁺ And Cd²⁺ From Oil-bearing Wastewater By Chestnut Shell And Bauhinia Husk

The oily wastewater discharged by industrial production contains not only oily pollutants but also heavy metal pollutants.If it is discharged into the environment,it will seriously pollute the ecological environment.So it needs to be effectively treated before discharging.In this study,we try to screen out appropriate adsorbing material for removing heavy metals from oily wastewater based on the agricultural and forestry wastes to replace activated carbon with high cost for the removal of heavy metals in oily wastewater.In this paper,an adsorbent was prepared from agricultural and forestry waste biomass as raw material,and a series of adsorption experiments were conducted based on simulated oily wastewater to screen out adsorbents with good adsorption performance of heavy metal ions(represented by Cu²⁺,Cd²⁺)for treating heavy metals in oily wastewater,and the optimal adsorption conditions were chosen.At the same time,the adsorption behavior of Cu²⁺and Cd²⁺on the adsorbents was studied by kinetic analysis and isothermal adsorption model,and the adsorption mechanism of the adsorbents was studied by their characterization analysis.The main findings are as follows:（1）The results of the static adsorption experiment of chestnut shell as an adsorbent showed that the optimal adsorption conditions for Cu²⁺and Cd²⁺removal from oil-containing wastewater were as follows:200rpm of the oscillator rate,the initial p H of the solution without adjusting（5.78）,25℃of the adsorption reaction temperature,60min of the adsorption reaction time,5 g·L^-1 of the adsorbent concentration,0.25-1mm of the particle size.As a result,the removal rate of Cu²⁺and Cd²⁺reached 93.9%and 92.4%,respectively,while the removal rate of emulsified oil was 42.5%.Through kinetic fitting analysis,it was found that the adsorption of emulsified oil in oily wastewater by chestnut shell fitted to the quasi-first-order kinetic model,and the adsorption of Cu²⁺and Cd²⁺by chestnut shell fitted to the quasi-second-order kinetic model.The results fitted by the isothermal adsorption model showed that the adsorption of Cu²⁺and Cd²⁺in the oily wastewater by chestnut shell fitted to the Langmuir isothermal adsorption model with a monolayer adsorption.Through dynamic adsorption experiments,it was found that the optimal adsorption penetration conditions of Cu²⁺and Cd²⁺in oily wastewater by chestnut shell were:the inlet water flow rate was 1.7 m L·min^-1 and the filling amount of the adsorption column was 2 g.（2）The results of the static adsorption experiment of bauhinia husk as adsorbent showed that the optimal adsorption conditions for Cu²⁺and Cd²⁺removal from oily wastewater were as follows:200rpm of the oscillator rate,the initial p H of the solution without adjusting（5.78）,25℃of the adsorption reaction temperature,60 min of the adsorption reaction time,5 g·L^-1of the adsorbent concentration,0.154-0.25 mm of the particle size.As a result,the removal rate of Cu²⁺and Cd²⁺by Bauhinia husk was 98.3%and 97.6%,respectively.The kinetic fitting analysis results showed that the adsorption of emulsified oil in oily wastewater by bauhinia husk fitted to the quasi-first-order kinetic model,and the adsorption of Cu²⁺and Cd²⁺fitted to the quasi-second-order kinetic model.Through the fitting of isothermal adsorption model,it was found that the adsorption of Cu²⁺and Cd²⁺by bauhinia husk fitted to the Freundlich isothermal adsorption model with a multilayer adsorption.Through dynamic adsorption experiments,it was found that the optimal penetration conditions for Cu²⁺and Cd²⁺in oily wastewater by bauhinia husk were:the inlet water flow rate was 1.7m L·min^-1,and the filling amount of the adsorption column was 2 g.（3）The comparison experiments of the static adsorption and dynamic adsorption among chestnut shell,bauhinia husk and activated carbon as the adsorbents found that the adsorption and removal effect of Cu²⁺and Cd²⁺by bauhinia husk and chestnut shell was better than that of activated carbon.Kinetics analysis showed that the adsorption rates of Cu²⁺were as follows:bauhinia husk(22.9 mg·（g·min）^-1)>chestnut shell(0.9 mg·（g·min）^-1)>activated carbon(0.3mg·（g·min）^-1).The adsorption rates for Cd²⁺were,in order,bauhinia husk(7.5 mg·（g·min）^-1)>chestnut husks(0.6 mg·（g·min）^-1)>activated carbon(0.09 mg·（g·min）^-1).The results of the study show that bauhinia husk and chestnut shells can replace activated carbon for the removal of heavy metals in oily wastewater.（4）The surface of Bauhinia husk and chestnut shells were characterized by SEM-EDS（Scanning Electron Microscopy-Energy Spectroscopy）and Zeta potentials.SEM-EDS results showed that the surface morphology of the two kinds of the material was rough and the structure was dispersed,which increased the surface adsorption site,showing that both materials had good adsorption properties;The Zeta potential results showed that the surface of both materials was negatively charged,and there was static electricity on the adsorption of Cu²⁺,Cd²⁺,so it had strong adsorption performance for heavy metal cations and poor adsorption performance for neutral emulsified oil molecules.