The Study Of Adsorption Efficiency Of Heavy Metal From Aquous Solution Using Modified Chinese Walnut Shell

The rapid development of industry, produces large amounts of toxic heavy metalwastewater. These waste on the environment have caused great harm to human healthand ecosystems. Therefore, removal of heavy metals from wastewater has become oneof the important environmental problems. The use of agricultural and forestry wasteadsorbent is a kind of new technology and utilization of biomass for removal of heavymetals in the water, because of its low cost, no environmental pollution, abundantsources, it has an advantage over other traditional method.This paper selects the agricultural and forestry waste material Chinese Walnutshell （MCWS） as raw material, through to the aqueous solutions of Cr⁶⁺, Cu²⁺, Hg²⁺,Cd²⁺single metal solution and the mixed solution of metal adsorption behaviorresearch, examines the MCWS adsorbent adsorption properties. The structure,morphology of MCWS were characterized using Fourier Transform InfraredSpectroscop（FTIR）, Specific Surface Area Analyzer, Elemental Analyzer and ScanningElectron Microscopy（SEM）. The optimum sorption conditions such as a metal solutionpH, initial concentration of metal ions, MCWS dosage, solution temperature andadsorption time,were studied. Adsorption mechanism were analysis using the modelon the adsorption kinetics and adsorption isotherm equation to the experimental dataanalysis.The FTIR showed that MCWS has many chemical group or chemical bond. Inthe wave number3423.3cm^-1peak is hydroxyl vibration, while in2937.5cm^-1absorption peak is the C-H stretching vibration of methylene.1738.4cm^-1is carboxylgroups on the carbonyl vibration.1638.2cm^-1is molecules inside of carboxyl groupson the carbonyl stretching vibration,1513.7cm^-1is on the aromatic ring of the C-Cstretching vibration.1462.6cm^-1is proved on the aromatic ring of the C-C stretchingvibration.1372.5to1046.2cm^-1are phenolic groups on C-O bond vibration, differentphenol based on a different C-O MCWS rich in tannin.605.7cm^-1is aromaticcompound vibration. These groups such as-OH and-COOH may be related to theadsorption of heavy metals.The adsorption of MCWS in aqueous solution of single metal experimental resultsshow that, Cr⁶⁺ion removal rate decrease with increased pH, the maximum removal rate in pH=1, can achieve82.88%; Cu²⁺ion removal rate increase with the increase ofpH value, the highest removal rate of pH5, removal rate can reach80.44%; Cd²⁺ionremoval rate increase with increasing of the pH, pH=7reaches the maximum95.64%; MCWS adsorption adsorption amount of Hg²⁺with pH increased, pH=5reaches the maximum adsorption rate of92.30%, then the adsorbed began to decline.Experimental data of adsorption of MCWS in aqueous solution of single Cr⁶⁺,Cu²⁺, Hg²⁺, Cd²⁺ion are consistent with the Langmuir adsorption model, Adsorptioncapacity of MCWS on Cr⁶⁺, Cu²⁺, Hg²⁺, Cd²⁺ion are as follows:41.7mg/L,15.87mg/L,8.06mg/L,37mg/L.Adsorption process of MCWS on aqueous solutions of Cd⁶⁺, Cu²⁺,Hg²⁺, Cd²⁺is consistent with the pseudo-second-order dynamic equation. Adsorptionprocess is quickly in the first short time, the adsorption equilibrium time is30-45min.Adsorption mechanism of MCWS were analysed using desorption experiment,FTIR, SEM.The results show that the adsorption mechanism of Cd⁶⁺adsorptionprocess is chemical adsorption,-OH,-COOH,H+and Cr⁶⁺ions by ion exchange andcomplexation in main adsorption process. Cu²⁺adsorption ion adsorption process iscontroled by chemical adsorption, the reaction is endothermic. The hydroxyl groupplay the main role in adsorption process of Cu²⁺ion through ion exchange, theformation of the new bond energy is low, easy to be destroyed. Cd²⁺ion adsorptionprocess is chemical adsorption, Cd²⁺ion and C=O undergo endothermic chemicalreaction, the new generation of chemical bonding is weak, easy desorption. Themechanism of Hg²⁺ion adsorption may be the the H+and Hg²⁺of hydroxyl groups ionby ion exchange, which belongs to the endothermic reaction, the newly formed key arelower.The optimum pH of adsorption of Cr⁶⁺, Cu²⁺, Hg²⁺, Cd²⁺mixed ion using MCWSis between5.0-7.0, the maximum adsorption rate of mixed Cr⁶⁺, Cu²⁺, Hg²⁺, Cd²⁺arelower than metal solution. The best time of adsorption is30-90min. As the metal ionconcentration increases, the adsorption rate decreased. The initial concentration of25mg/L can reach maximum adsorption rate. Mixed metal ion adsorption rate increaseswith the rise of temperature, mixed metal best adsorption temperature is30.MCWS on the adsorption process of mixed metal solutions for Langmuir equation, thedescription of the adsorption process for the uniform monolayer adsorption. Cr⁶⁺, Cu²⁺,Hg²⁺, Cd²⁺maximum adsorption is18.24mg/L,12.8mg/L,7.12mg/L,13.32mg/L, wereless than single metal adsorption process. Mechanism ofadsorption of Cr⁶⁺, Cu²⁺, Hg²⁺, Cd²⁺mixed ionic by MCWS involves a number of chemical groups such as-COOH,-OH or chemical bonding, C-H, C-O by ion exchange or complexation adsorption.