Study Of Recovery And Utilization Of Heavy Metal By Adsorbent And Catalyst Supports Microspheres From Geopolymer

With the rapid development of industrialization and modernization,water pollution of heavy metals such as Cu,Ni,Co is becoming more and more serious,and most of these heavy metals are valuable and high-demand metals.Although the removal of heavy metals in wastewater is a concern for environmental protection,the ability to recover and use heavy metals in wastewater is also the inevitable requirement of green circular economy.In this study,the NaOH or KOH activated slag-based geopolymer microsphere adsorbents（NaOH-SGS or KOH-SGS）were prepared by the suspension solidification method.The geopolymer application systems of“geopolymer—adsorbent—catalysts after adsorption”and“the recovery of heavy metal—the water pollution treatment—the air pollution treatment”were constructed.The problems of the problems of difficult recovery and secondary environmental pollution of the current adsorbents were solved.A new research idea of environmental protection and recycle the heavy metal was proposed.The main conclusions are as follows:（1）The formula for preparing the best adsorption capacity of Cu（Ⅱ）or Co（Ⅱ）on the NaOH or KOH activated slag-based geopolymer microsphere adsorbent（NaOH-SGS or KOH-SGS）prepared by the suspension solidification method were obtained.When C₀=300 mg/L,0.15 g/100 m L,25°C and p H=5,the best formula for NaOH-SGS to adsorb Cu（Ⅱ）is:n（Na₂O）/n（Al₂O₃）=1.5,n（H₂O）/n（Na₂O）=18.When C₀=200 mg/L,0.04 g/100 m L,25°C,p H=7,the best formula for MOH-SGS（M=Na、K）to adsorb Co（Ⅱ）is:n（M₂O）/n（Al₂O₃）=1.5,n（H₂O）/n（M₂O）=18.The adsorption capacites of KOH-SGS and NaOH-SGS for Co（Ⅱ）are obviously different.（2）The Cu（Ⅱ）adsorption performance on NaOH-SGS was investigated in detail.NaOH-SGS has a good Cu（Ⅱ）adsorption capacity(Q_Cu=335.43 mg/g),which was better than other reported geopolymer adsorbents’.The adsorption process of NaOH-SGS on Cu（Ⅱ）was a spontaneous,endothermic and preferential adsorption,and it was mainly controlled by the external boundary layer diffusion.It mainly conformed to the pseudo-second-order kinetics and Langmuir isotherm model.Meanwhile,the specific surface area change process during the adsorption process of NaOH-SGS on Cu（Ⅱ）was an adsorption process of self-growth heavy metal.The supported catalyst was prepared by calcining NaOH-SGS which had adsorbed Cu（Ⅱ）（NaOH-SGS-Cu-calcined）and then was used in the catalytic reduction of NO by CO.At atmospheric pressure and 350°C,it exhibits good catalytic activity(NO conversion rate(X_NO)is91.96%)and N₂ selectivity(S_N2)is 78.15%).（3）The Ni（Ⅱ）adsorption performance on NaOH-SGS was investigated in detail.NaOH-SGS had good adsorption capacity(Q_Ni=414.38 mg/g)which was better than other reported geopolymer materials’.At the same time,the possible mechanism of self-growth heavy metal adsorption process was proposed.The adsorbed Ni（Ⅱ）NaOH-SGS（NaOH-SGS-Ni）was used in the catalytic reaction system of CO₂ hydromethanation.Although the optimal temperature for CO₂conversion(X_CO2,99.54%)and CH₄ selectivity(S_CH4,99.5%)was 300oC,the catalyst exhibited excellent catalytic activity(X_CO2 is 99.48%and S_CH4 is 98.2%)at low temperature（100oC）and ordinary pressure.（4）The behavior competitive adsorption among Cu（II）,Ni（II）and Co（II）on NaOH-SGS was investigated in detail.In single-solute systems,NaOH-SGS has high adsorption capacity(Q_Cu（311.21 mg/g）,Q_Ni（191.17 mg/g）and Q_Co（101.02mg/g）).Regardless of the single or multiple-solute systems,the order of their adsorption capacity is:Cu（II）>Ni（II）>Co（II）.In addition,the adsorption capacities in the multiple-solute systems were lower than that in the single-solute systems.The adsorption process was in accordance with the pseudo-second-order kinetic and Langmuir models in the single-solute systems.For Cu Ni-and Cu Co-solute systems,the adsorption processes fit pseudo-second-order kinetics well;but for Ni Co systems,the adsorption process fit pseudo-first-order kinetics well.All binary-solute systems conformed to the modified Langmuir model.The change process of the specific surface area of NaOH-SGS after adsorption belongs to the process of self-growth heavy metal adsorption.The atomic orbital energy and electron spin state of Cu,Ni and Co,the structural fitness between NaOH-SGS and heavy metals（Cu（II）,Ni（II）or Co（II）in this study）,atomic radius of Cu（II）,Ni（II）or Co（II）,electronegativity of MOH-SGS and bond valence parameters R₀,etc.could properly explain the competitive adsorption behavior and mechanism among Cu（II）,Ni（II）and Co（II）on NaOH-SGS.And the NaOH-SGS after heavy metal ions adsorption were labled as NaOH-SGS-M,M=Cu,Ni,Co,Cu Ni,Cu Co,Ni Co,Cu Ni Co.And these NaOH-SGS-M were calcined to be catalysts which were applied in the catalytic reduction NO by CO.At 350℃,the catalytic activity of NaOH-SGS-Cu-calcined for catalytic reduction of NO by CO is 91.96%and78.15%for X_NO and S_N2 respectively.At 650-700℃,the X_NO and S_N2 of calcined NaOH-SGS-Ni,NaOH-SGS-Cu Ni,NaOH-SGS-Cu Co and NaOH-SGS-Cu Ni Co all reached nearly 100%.（5）The significant difference in Co（II）adsorption capacity between NaOH-SGS and KOH-SGS(Q_e,NaOH-SGS=91.21 mg/g,Q_e,KOH-SGS=192.31 mg/g)was systematically studied.The change process of the specific surface area of NaOH-SGS after adsorption belongs to the process of self-growth heavy metal adsorption.The hydrated ion radius of K and Na,the alkalinity of K⁺and Na⁺,the Zeta potentials of the surface of NaOH-SGS and KOH-SGS,the change of the BET surface area and CO₃^2-in FT-IR between before and after Co（II）adsorption,and XPS analysis were the reasons of this obvious difference.Although the catalyst which was prepared by calcining KOH-SGS after Co（Ⅱ）adsorption（KOH-SGS-Co-calcined）was used in the catalytic reduction NO by CO..At 700℃,the catalytic activity of KOH-SGS-Co-calcined(X_NO,S_N2,Y_N2were 12.3%,100%and 12.3%respectively)was nearly one half of that of NaOH-SGS-Co-calcined(X_NO=6.85%,S_N2=97.02%and Y_N2=6.65%).（6）The adsorption conditions for Co（Ⅱ）on KOH-SGS was simulated and optimized by the Response Surface Methodology（RSM）which had a good fit because of R²=0.9931.KOH-SGS had a good adsorption capacity(Q_Co=211.26 mg/g)which was better than other reported geopolymers materials’.The change process of the specific surface area of NaOH-SGS after adsorption belongs to the process of self-growth heavy metal adsorption.The Co（Ⅱ）adsorption process on KOH-SGS was a spontaneous,endothermic and preferential adsorption process.It mainly controlled by external boundary diffusion and fit the pseudo-second-order kinetic,Langmuir isotherm model well.To recover the cobalt,the adsorbed Co（Ⅱ）KOH-SGS（KOH-SGS-Co）was applied in CO₂ methanation.The activity of CO₂ hydrogenation(X_CO2=57.63%)was better than the activity of catalytic reduction of NO(X_NO=12.3%).