| In China,waste slags containing arsenic(As)produced from non-ferrous metal smelting and the sludge produced from water treatment have become the main As pollution sources.The most important treatment and disposal way is safe landfill after immobilization.The core of immobilization technology lies in the selection of materials.Due to the different pollution characteristics of waste slgs produced from different smelting industries,the research on immobilization mechanism and applicability of different materials is still needed,the feasibility study of As(Ⅲ)preoxidation technology to enhance As immobilization effect should also be strengthened.In this study,waste slags containing As produced from copper smelting,lead-zinc smelting and pyrite smelting industries and sludge containing high As produced from the acid making industry were treated by different immobilizing materials,different risk scenarios were simulated,and the immobilization effects of different materials were studied.The As immobilization mechanism of typical materials was revealed by means of XRD,SEM,XPS and other micro characterization means.The technology of As(Ⅲ)oxidation was studied to strengthen the As immobilization effect in slag mainly containing As(Ⅴ)and sludge mainly containing As(Ⅲ).This thesis provided scientific basis for the engineering application of different immobilizing materials in waste slags containing As produced from different smelting industries and sludge produced from water treatment process.The main results were as follows:(1)Ten kinds of typical materials including sulfides,calcium-based and iron-aluminum-based materials(Fe0,ferric salt,Fe2O3/Al2O3)were used to immobilize the waste slag of copper smelting industry.Five single chemical extraction methods simulating different exposure conditions were used to screen out materials with better immobilization effect.The mechanism underlying As immobilization by typical materials was revealed by the analysis of continuous chemical extraction and microstructure characterization.The results demonstrated that Na2S·9H2O showed the best immobilization effect under natural condition.While,Fe0 exhibited the strongest As stabilization ability followed by FeSO4·7H2O under other conditions.Fe0 is suitable for As immobilization under organic weak acid and strong acid rain conditions.FeSO4·7H2O was effective under all conditions,however its effect varied greatly.It showed the best effect for As immobilization under weak organic acid condition,and TCLP-As leaching was reduced to 1.50 μg·L-1 with As immobilization rate of 99.98%.FeSO4·7H2O mainly reduced the extractable weak acid state,and converted the non-specific/specific adsorption state,amorphous and weak crystalline iron-aluminium or iron-manganese state into crystalline iron-aluminium or iron-manganese state and residue state.A small amount of insoluble iron and arsenic minerals(FeAsO4·2H2O and FeAsS)were formed after treatment.(2)Several kinds of immobilizing materials such as typical sulfides,phosphorus-containing,calcium-containing,magnesium-containing,clay minerals were used to immobilize two kinds of Zn and Cd polluted waste slags of lead-zinc smelting industry.The effects of different materials on the coexistence of As in slags were also investigated.The immobilization effect was evaluated by H2SO4-HNO3 leaching method.The immobilization results of 1#slag showed that:Na2S·9H2O,Na3PO4 12H2O,CaO,MgO,bentonite had obvious immobilization effect on Zn and Cd,but the application of phosphorus-containing materials made As leaching detected.The results of 2#slag showed that the immobilization effects of Zn,Cd and As were Na2S·9H2O>Na3PO4·12H2O>(NH4)2HPO4,Na3PO4·12H2O and(NH4)2HPO4 were easy to activate As,although they had high immobilization efficiency for Zn;MgO was better than CaO,the MgO immobilization rates for Zn,Cd,As reached 86.99%,91.37%,90.88%respectively at 1%dosage.MgO and Na2S·9H2O were the best immobilizing materials.(3)Typical sulfides,phosphates,CaO,MgO and compatible reagents were used to immobilize the strong acid slag of pyrite smelting industry polluted by Zn and Cd.The immobilization effect was evaluated by water extraction(HJ 557-2010).The maximum allowable discharge concentration of GB 8978-1996 was taken as the standard requirement.The results showed that the same molar addition ratio of single phosphate and sulphide was obtained.Under these conditions,Na3PO4·12H2O had the best immobilization effect on Zn and Cd,Na2S·9H2O had the best immobilization effect on As,and the comprehensive immobilization effect of the 4 elements simultaneously reaching the standard is 2.42%Na2S·9H2O(η=96.36%)>0.64%(NH4)2HPO4(η=87.42%)>0.46%Na3PO4·12H2O(η=82.26%).The comprehensive immobilization effect of single MgO or CaO and combination agent was 0.4%MgO>0.4%CaO>(0.4%CaO+0.61%Na2S·9H2O)>(0.4%CaO+0.32%(NH4)2HPO4)>1.2%(Na2S·9H2O:(NH4)2HPO4:Na3PO4·12H2O=2:1:3).MgO,Na3PO4·12H2O and calcium-sulfide were the best immobilizing materials.(4)Ten kinds of materials,including sulfide,calcium-based material and several iron-aluminum-based materials(Fe0,ferric salt,Fe2O/Al2O3),were used to immobilization high As(III)-bearing sludge.The As immobilization effect of the selected materials was investigated by TCLP(toxicity characteristic leaching procedure),H2SO4-HNO3 and H2O together with the influence of immobilization on the valence and binding form distribution of As in sludge.Then the optimal material for As immobilization was achieved,which was used for the later cement mixed solidification study.The screening result of materials show that FeCl3 had the best As immobilization effect,and the As immobilization percent η(As)were 86.01%,42.02%,58.87%,respectively.The addition of FeCl3 and Fe0 significantly enhanced the transformation of As from unstable speciation into stable speciation,and specifically,the proportion of non-specifically bound As fraction and specifically bound As fraction decreased by 80.60%and 38.13%respectively.Besides,the FeCl3 promoted the transformation from non-specifically and specifically bound As fractions to crystalline hydrous Fe(Mn,Al)oxide fraction and residual fraction.Six materials could oxide As(Ⅲ)to As(Ⅴ).Among them,the proportion of As(Ⅲ)with addition of FeCl3 decreased maximally from 77.14%to 19.72%.The oxidation of As(Ⅲ)by Fe(OH)3,Fe2O3 and Al2O3 treatment was not apparent.However,due to the strong reducibility of Na2S·9H2O,the proportion of As(Ⅲ)after adding Na2S·9H2O increased to 85.84%.As the amount of FeCl3,cement and composite materials increased,the leaching toxicity of As in sludge decreased significantly.The As immobilization effect of single FeCl3 and FeCl3+cement treatments were better than that of single cement treatment.When the cement ratio was set to above 100%,the As immobilization effect of treatment was better than that of single cement treatment.The leaching concentration of TCLP,H2SO4-HNO3 and H2O in 250%FeCl3+125%cement treatment decreased maximally to 113.81 mg·L-1,399.28 mg·L-1 and 347.27 mg·L-1,respectively.The arsenic immobilization percent was above 97%.(5)The results of As(Ⅲ) oxidation strengthening As immobilization effect were shown below:Six kinds of oxidation treatments were carried out on high As(V)-containing slag,30%H2O2,KMnO4 and Na2S2O8 were found to be good oxidizers.Four kinds of oxidation treatments were carried out on high As(Ⅲ)-bearing sluge,KMnO4 was found to be good oxidizer,The decreasing rate of As(Ⅲ)percentage in oxidation treatments is KMnO4(39.66%)>MnO2(25.51%)>Na2S2O8(10.67%)>H2O2(7.04%).KMnO4 decreased the concentration of As(Ⅲ)and total As concentration in TCLP and H2SO4-HNO3 leaching solution,but increased As concentration by 0.61%in H2O leaching solution,and only reduced the proportion of As(Ⅲ)by 3.05%.All treatments reduced the bioavailability of As,but increased the plant availability of As.Each treatment significantly increased the percentage of F1+F2 by Wenzel method,and significantly increased the risk of arsenic release except for KMnO4,and KMnO4 had the lowest risk. |
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