Study On The Adsorption Performance Of Tetratitanate Nanowhiskers For Ni²⁺ In Aqueous Solution And Electroplating Wastewater

In this paper,the preparation of tetra titanate nanowhiskers,the adsorption characteristics of tetra titanate nanowhiskers to Ni²⁺in aqueous solution and the characteristics of oxidation adsorption of Ni²⁺in electroplating wastewater were studied.（1）Tetra titanate nanowhiskers were prepared by hydrothermal method.The adsorption kinetics,adsorption isotherm and thermodynamic properties of tetra titanate nanowhiskers for Ni²⁺in aqueous solution were studied.（2）The effect of calcium hypochlorite and sodium hypochlorite oxidants on reducing chemical oxygen demand（COD）of nickel containing electroplating wastewater,and the effect of tetra titanate nanowhiskers on adsorption of Ni²⁺in electroplating wastewater after oxidation and breakdown were studied.（3）The adsorption kinetics,adsorption isotherm and thermodynamic properties of calcium hypochlorite or sodium hypochlorite oxidant used to oxidize nickel containing electroplating wastewater,combined with tetra titanate nanowhiskers,to adsorb Ni²⁺from electroplating wastewater were studied.With the intermediate metatitanic acid（H₂Ti O₃?n H₂O）and sodium hydroxide in the production of titanium dioxide by sulfuric acid method as raw materials,the average diameter and average length of 448 nm and 8.38 nm,respectively,were hydrothermally synthesized at180℃μM layered tetra titanate(Na_0.98H_1.02Ti₄O₉?3.3H₂O)nanowhiskers.The specific surface area,pore volume and average pore diameter of tetra titanate nanowhiskers are 91m²/g,0.25 m L/g and 9.8 nm,respectively.The large specific surface area and pore size provide more active site for the adsorption of Ni²⁺from aqueous solution,and reduce the diffusion resistance of Ni²⁺in the pores.In the study of adsorption of Ni²⁺from aqueous solution by tetra titanate nanowhiskers,it was found that the adsorption of Ni²⁺on tetra titanate nanowhiskers conformed to the quasi second order adsorption kinetic model.The Langmuir adsorption model was used to fit the experimental data.It was found that the maximum adsorption capacity of tetra titanate nanowhiskers for Ni²⁺at p H 7 and 20?50℃was between 146.4 and 175.4 mg/g.In the process of adsorption of Ni²⁺from aqueous solution by tetra titanate nanowhiskers,ΔG<0,ΔH>0 andΔS>0。This indicates that the adsorption of Ni²⁺by tetra titanate nanowhiskers from aqueous solution is a spontaneous and endothermic process,and the adsorption of Ni²⁺is a disorderly increase process.When the actual industrial electroplating wastewater(Ni²⁺,0.28mg/L;COD,280 mg/L)with Ni²⁺complex is oxidized by calcium hypochlorite（Cl O^–,0.3496mol/L）and sodium hypochlorite（Cl O^–,0.282 mol/L）respectively for 3 h,and then four titanate nanowhiskers（133.3 mg/L）are used to adsorb Ni²⁺in the electroplating wastewater after oxidation and breakdown for 4 h,the concentration of Ni²⁺in the electroplating wastewater after oxidation and adsorption treatment is reduced to 0.045 mg/L and 0.064 mg/L respectively.The content of Ni²⁺in electroplating wastewater after oxidation of calcium hypochlorite and adsorption treatment of tetra titanate nanowhiskers reaches the emission limit of Ni²⁺（0.05 mg/L）in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants（GB18918?2002）.Hypochlorite as oxidant,tetra titanate nanowhisker as adsorbent,and simultaneous adsorption treatment of nickel containing industrial electroplating wastewater in the process of oxidation and breakdown,it was found in the study that at 15°C,sodium hypochlorite（Cl O^–,0.012?0.229 mol/L）or calcium hypochlorite（Cl O^–,0.01399?0.27972 mol/L）as oxidant,tetra titanate nanowhisker（74?80 mg/L）as adsorbent,When simultaneously oxidizing/adsorbing Ni²⁺(Ni²⁺,0.08?0.24 mg/L)in electroplating wastewater,the adsorption amount of Ni²⁺increases with the increase of adsorption temperature and oxidant dosage.Langmuir adsorption model was used to fit the experimental data.The concentration of sodium hypochlorite was 0.229 mol/L,the adsorption temperature was 15 to 50 ^oC,and the maximum adsorption capacity of tetra titanate nanowhiskers for Ni²⁺was 1.0452?1.2950mg/g.The concentration of calcium hypochlorite is 0.13986 mol/L,the adsorption temperature is 15?50℃,and the maximum adsorption capacity of tetra titanate nanowhiskers for Ni²⁺is 1.4751?1.9932 mg/g.At the same Cl O^–concentration,calcium hypochlorite has stronger oxidizing properties than sodium hypochlorite,improving the effect of oxidation/adsorption for removing Ni²⁺from electroplating wastewater.Ca（Cl O）₂（Cl O^–,0.27972 mol/L）and Na Cl O（Cl O^–,0.229 mol/L）,When calcium hypochlorite is used as an oxidant,the electroplating wastewater undergoes simultaneous oxidation/adsorption treatment to meet the discharge standard of total nickel≤0.1 mg/L specified in the"Electroplating Pollutant Discharge Standard"（GB21900?2008）.The large amount of organic matter present in electroplating wastewater also poses serious harm to the environment.In the study of simultaneous adsorption treatment of electroplating wastewater（COD,136 mg/L）during the oxidation process,it was found that when Ca（Cl O）₂（Cl O^–,0.27972 mol/L）and Na Cl O（Cl O^–,0.229 mol/L）were used as oxidants,the COD values of electroplating wastewater after oxidation/adsorption treatment decreased to 43.9 and 71.9 mg/L,respectively.Among them,when Ca（Cl O）₂（Cl O^–,0.27972 mol/L）is used as an oxidant,it meets the discharge standard of COD<50 mg/L in the Chemical Industry Water Pollutant Discharge Standard（DB32/939?2020）.At the same Cl O^–concentration,Ca（Cl O）₂ exhibits slightly higher oxidation ability than Na Cl O for the organic components in actual electroplating wastewater with the same composition.With calcium hypochlorite or sodium hypochlorite as oxidant and tetra titanate whisker as adsorbent,general industrial electroplating wastewater is oxidized and adsorbed.After treatment,the residual Ni²⁺concentration meets the discharge threshold of urban wastewater or industrial electroplating wastewater authorized by the Ministry of Ecological Environment of China.The oxidation and adsorption methods for treating practical industrial electroplating wastewater containing refractory Ni²⁺complexes have good industrial application prospects.