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Sorption of Copper Ion on Several Fe, Al, Mn-Oxides and Humic Components

Author: WangShuai
Tutor: ZuoSen；ZhangJinJing
School: Jilin Agricultural University
Course: Soil
Keywords: humic components oxide copper ion sorption EXAFS
CLC: X53
Type: Master's thesis
Year: 2008
Downloads: 180
Quote: 1
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Abstract

The accumulation of heavy metal in soil environment is an important environment problem which the world men face.Cu²⁺ isn’t only an essential nutritive element that the plant growth needs,but also an extremely common pollutant in the environment.The ecology toxicity in which excessive Cu²⁺ results in the soil environment will restrain the plant photosynthesis, which can cause the reduction of yield,simultaneously,threaten ecosystem’s security and the human health.The soil adsorption phenomenon is an extremely complicated physical,chemical process. The adsorption is the first process that Cu²⁺ enters the soil.The iron,aluminum,manganese oxides（goethite,hematite,bayerite andδ-MnO₂ and so on） and humic components（humin, humic acid and fulvic acid） can greatly affect the migration and end-result of microelements in the soil.The adsorption of metal ion on soil always occurs in the different environmental conditions,such as the ionic strength,the pH value,the temperature,whose change will have an influence to the adsorption of metal ion.In view of the above questions,the batch equilibrium technique was applied to study the adsorption of dark-brown soil,synthesized oxides（goethite,hematite,bayerite andδ-MnO₂）, crude humin,humic acid and crude humin（add humic acid or fulvic acid） to Cu²⁺ at different the pH values（2-8）,ionic strengths（NaNO₃ 0.1～1.0mol/L）,temperatures（25～45℃） and contacting times（10～1440min）.By the Freundlich,Langmuir and Temkin equation fitting the thermodynamical adsorption process,the thermodynamical parameters（ΔG、ΔH、ΔS） were calculated using Langmuir’s constant.We also applied Elovich,the first-level dynamic equation, the double constant equation and the parabola diffusion equation in figuring out the activation energy（E） and the thermodynamical activation parameters（ΔG^#、ΔH^#、ΔS^# ） to explore the adsorption rules and differences from them.That will be helpful in clarifying the migration and the plant validity of Cu²⁺ in the soil and executing microelements’ fertilizer reasonably in different time and places.The theory basis was supplied to formulate environmental capacity and prevent the pollution from Cu²⁺.Through the above researches,this article draws the following conclusion:（1） The adsorption rate of Cu²⁺ increased with an increase of solution pH.When the solution pH is 8,the adsorption rate can almost achieve 91%;With an increase of ionic strength, the adsorption of Cu²⁺ reduces firstly,and then increases;The amount adsorbed increased with an increase of the Cu²⁺ concentration,and increased rapidly at low concentration.The Langmuir model was better than the Freundlich and Temkin models for describing the Cu²⁺ adsorption isotherms.According to Langmuir model’s k_L value,we can calculate the thermodynamic parameters.They can tell us that the reaction is a spontaneous and endothermic process,but its disorder is the same;The kinetics of adsorption experiment could be divided into two stages, rapid and slow adsorption,and the dual-constant model can be the best model that used to describe the Cu²⁺ adsorption rate on dark-brown soil.According to the first-order kinetic model’ k_D value,we cannot only figure out activation energy and thermodynamics parameter,but also confirm a fact that increasing temperature is propitious to improve the reactive rate.（2） The adsorption of Cu²⁺ increased with an increase of solution pH from 2 to 8.The threshold pH values of Cu²⁺ adsorption were 4,5 and 4 for goethite,hematite and bayerite respectively,however,it was not obvious forδ-MnO₂.With an increase of ionic strength,the adsorption of Cu²⁺ increased on goethite and hematite while it decreased onδ-MnO₂ and bayerite.The amount adsorbed increased with an increase of the Cu²⁺ concentration.The Langmuir model was better than the Freundlich and Temkin models for describing the Cu²⁺ adsorption isotherms.The adsorption processes of Cu²⁺ were spontaneous and endothermic with higher disorder.The adsorption of Cu²⁺ could be divided into two stages,rapid and slow adsorption,and the Elovich model can be used to describe the Cu²⁺ adsorption rate on goethite andδ-MnO₂,the dual-constant and parabola model for hematite and the first-order kinetic model for bayerite respectively.The activation energy（E） and the activation thermodynamic parameters（ΔG^#,ΔH^#,ΔS^#） indicated that Cu²⁺ adsorption had the least energy requirement and the highest adsorption rate onδ-MnO₂,while the greatest energy requirement and the lowest adsorption rate were appeared on hematite.In general,the adsorption affinity of these oxides to Cu²⁺ were in order ofδ-MnO₂＞bayerite＞goethite＞hematite.（3） The adsorption of Cu²⁺ on crude HM increased with increasing initial pH from 2～7 and decreased with increasing ionic strength from 0.01～1.00mol·L^-1.Cu²⁺ was retained on HM fraction by both non-specific and specific bonding.The adsorption capacity of Cu²⁺ on HM fraction increased with the temperature and Cu²⁺ concentration.The Langmuir isotherm fitted the experimental results better than did the Freundlich and Temkin isotherm.The maximum Cu²⁺ adsorption capacity of crude HM was 12.61mg·g^-1 at 25℃and 14.31mg·g^-1 at 45℃. Adsorption kinetics of Cu²⁺ on crude HM consisted of a rapid reaction（0～120min） followed by a slow one（120～1440min）.And the kinetic processes could be best described by the parabolic diffusion models model.Characteristics of Cu²⁺ adsorption on crude HM were basically identical to those of HA,while the adsorption capacity of the former was lower.The apparent thermodynamic parameters（ΔG,ΔH,ΔS） indicated that the adsorption of Cu²⁺ on crude HM was spontaneous,endothermic and increasingly confused process;desorption of Cu²⁺ from HM fraction was more difficult than that from HA.Based on values of the energy of activation（E） and thermodynamic parameters of activation（ΔG^#、ΔH^#、ΔS^#）,Cu²⁺ adsorption rate on crude HM was slower than that on HA.The presence of HA or FA could increase the adsorption of Cu²⁺ to crude HM.（4） The microscopic local structure of Cu²⁺ in Cu（NO₃）₂ solution under different pH conditions was identical,and the coordination number（N）,bond length（R） and thermal disorder parameter（σ_t²） were respectively 4.3～4.4,1.95～1.96（?） and 0.0056（?）2 for the Cu-O first neighbor shell.The Jahn-Teller effect which make the axial Cu-O bonds are difficult to characterize quantitatively by EXAFS spectroscopy was responsible to the EAXFS results of Cu²⁺.The coordination peak of Cu-Cu had not been detected at pH 2,but it occurred at about 2.40（?）,at pH 8,indicated that the formation of Cu（OH）₂ precipitate under the condition of pH 8. Before the adsorption of Cu²⁺ onto goethite,the N,R andσ_t² were respectively 6.2,1.98（?） and 0.0083（?）² for the Fe-O first neighbor shell in goethite.The N and R of Fe-O were identical to initial goethite after the adsorption of Cu²⁺ onto goethite,butσ_t² of its increased.

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