| In recent years, the increasing incidence of heavy metal pollution seriously affects people's physical and mental health, the State Environmental Protection Bureau said that by 2010 China would focus on comprehensive improvement of heavy metal pollution. In this study, searching for inexpensive and effective adsorbent is the principal purpose, in order to solve the problems of energy consumption, secondary pollution and high cost which exist in traditional heavy metal wastewater treatment methods. Agricultural and forest residues are by-products in agricultural, forestry production and processing,with the advantages of low cost, large output, renewable,short regeneration cycle, biodegradable and environmental-friendly and so on, it is an important biomass resources. But its utilization is less than 50% of total amount,if agricultural and forestry residues are used in treating industrial waste water, not only would waste water pollution reduce,but could make full use of renewable resources, to achieve the goal of treatment by waste,and significantly reduce the treatment cost. This study is divided into four parts:(1) Selection test:this adsorbent which was selected from eight agricultural and forest residues materials should have the ability of high Cr(Ⅵ) and total Cr removal efficiency, less organic matter exudation (TOC), than physical and chemical properties of adsorbent would be analyzed.(2) Reseaching the Cr(Ⅵ) adsorption and desorption characteristics by preferred adsorbent from wastewater:The affecting factors of removal efficiency such as adsorbent particle size, pH, temperature, Cr(Ⅵ) initial concentration and adsorbent dosage were investigated, adsorption kinetics and thermodynamics were analysised, and adsorbent with Cr(Ⅵ) binding mechanism was probeed by infrared spectroscopy(3) Reseaching the Cu2+, Zn2+, Pb2+ adsorption and desorption characteristics by preferred adsorbent from wastewater. The affecting factors of removal efficiency such as pH, adsorbent dosage, reaction time, initial concentration were investigated, and desorption effect of equilibrium adsorbent under different pH was studied.(4) Using the actual electroplating wastewater as adsorption object, heavy metal ions removal efficiency was tested by preferred adsorbent.Based on the analysis and compassion of the test data, we can get the conclusions, the result shows:(1) Selection test showed pine cone was the preferred adsorbent from eight agricultural and forest residues materials. Under the conditions (Cr(Ⅵ) initial concentration 50mg/L, pH=2.0, temperature 30℃, adsorbent concentration 2g/L, reaction time 4h) removal rate of Cr(Ⅵ) was 100%, total Cr was 77.29%,and organic exudation amount was 26.01 mg/L by pine cone powder adsorbent.(2) Cr(Ⅵ) adsorption experiments showed that:pine cone powder was a good adsorbent material for Cr(Ⅵ),under the condition of the temperature 30℃, adsorbent dosage 3g/L, particle size 120 mesh, Cr(Ⅵ) concentration about 50mg/L, Cr(VI) removal rate reached 100% within 15 minutes at pH=2, which reaching 80.6% within 2 hours at pH=3. Under the experimental conditions, The Cr(Ⅵ) removal rate increased with the decrease of the size of adsorbent,pH and initial Cr(Ⅵ) concentration, and with the increase of adsorbent dosage and temperature.Freundlich and Langmuir isotherms were used to fit the adsorption equilibrium data and the adsorption p rocess followed the Freundlich isotherm adsorption model.According to the desorption experiment under different pH, the binding energy of pine cone with Cr is very high, just when pH=11 a small quantity of Cr(VI) was desorpted. FTIR analysis indicated that amino, hydroxy, carboxyl and vitriol groups are the main functional grops in the reaction with Cr.(3) Adsorption experiments of Cu2+,Pb2+,Zn2+ showed that when pH between 5～5.5, initial concentration of heavy metal ions was 25mg/L, the optimum dosages of adsorbent for Pb2+,Cu2+, Zn2+ were 3,1.5,3g/L respectively. The time-dependent asorption data were well-described by Lagergren-second-order kinetic model, all R2 exceed 0.998. Langmuir and Freundlich sorption isotherm were applied to describe the absorption behavior, and the maximum adsorption capability of Pb2+,Cu2+ and Zn2+ by pine cone were 9.10,31.95 and 9.60 mg/g respectively.Strong acid was a perfect desorbent for Cu2+ and Zn2+.(4) Adsorption results from the actual electroplating wastewater showed that:ure pine cone was a good adsorptive material, under the condition of pH=1.48, temperature 25℃, adsorbent concentration 3g/L,time 4h, removal rate of Cr(Ⅵ) was 100%. Then control the condition to pH=5.0, adsorbent concentration 5g/L, time 1h heavy metal ions can achieve the first discharge standard (GB8978-1996)...
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