Preparation Of Layered Metal Hydroxide And Treatment Of Laboratory Wastewater Containing Chromium

With the production,scientific research,teaching process of inspection department,research institute,university etc,more and more wastewater is discharged from laboratory,and the composition is more and more complicated,which has a serious impact on the ecological environment.Chromium is a common contaminant in laboratory wastewater.The Chinese National Integrated Wastewater Discharge Standard(GB 8978-1996)has made clear regulation that Cr(VI)concentration is less than 0.5 mg/L and total Cr is less than 1.5 mg/L in wastewater.Layered metal hydroxide,also known as anionic layered functional material,is used as adsorbent,especially for anion adsorption owning to its particular physical and chemical properties.Current research mainly used layered metal hydroxide to remove Cr(VI)in the wastewater,less involved in Cr(III)pollution treatment,rarely applied to the practical wastewater too.Therefore,removal effect of chromium was studied by a series of layered metal hydroxide prepared by coprecipitation.The main research works and achievements are as follows:(1)The Mg/Al layered metal hydroxide was prepared using Na2CO3/NaOH,NaOH and NH4 OH as precipitants.The Cr(VI)adsorption property of materials were compared using laboratory wastewater containing Cr(VI)as treatment object.The structure of materials was also discussed.Mg/Al layered metal hydroxide had higher crystallinity,perfect layered structure,larger specific surface area,suitable pore distribution and better removal rate of Cr(VI)by using Na2CO3/NaOH as the precipitator.The optimal absorption efficiency of Cr(VI)by calcined Mg/Al-LDH(Mg/Al-LDO)could be reached when pH values was 7~9,solid-liquid ratio was 1:500,meanwhile,the whole process reacted at room temperature for 9 h.The saturated adsorption capacity of Mg/Al-LDO was 199.41 mg/g under the optimal conditions.Mg/Al layered compounds was an excellent recycling ability.(2)Laboratory wastewater containing Cr(VI)was treated by the preparation of Mg/Al layered metal hydroxide in situ.The structure of material and removal mechanism of Cr(VI)were studied in combination with X-ray diffraction,Fourier transform spectrum,Thermo gravimetric/differential thermal analysis,N2 adsorption-desorption and Pore size of distribution curves.The optimal removal process of Cr(VI)was as follows: Mg/Al mole ratio was 2:1,pH value was 9~10,the reaction lasted for ten minutes at room temperature.The material was Mg(II)/Al(III)layered metal hydroxide containing Cr(VI).The Mg(II)and Al(III)hydroxide contributed the laminate of materials,the Cr(VI)selectively intercalated into interlayer of layered metal hydroxide by electrostatic attraction,and neutralized surface positive charge of laminate.Cr(VI)was removed as an interlayer anion.(3)Mg/Al/Fe(II)layered metal hydroxide(Mg/Al/Fe(II)-LDH)had been fabricated and used to remove Cr(VI)in laboratory wastewater depending on the redox function between Fe(II)and Cr(VI).The physicochemical properties of the materials were studied in combination with X-ray diffraction,Fourier transform spectrum,Thermo gravimetric/differential thermal analysis,N2 adsorption-desorption,Pore size of distribution curves and SEM.Mg/Al/Fe(II)-LDH was prepared with Mg(II):Al(III):Fe(II)molar ratios of 5:2:1 and aging at 80 ?C for 24 h.The optimal removal process of calcined Mg/Al/Fe(II)-LDH(Mg/Al/Fe(II)-LDO)for Cr(VI)was as follows: pH values was 9~10,the adsorption was at room temperature for 100 min.It was found that the saturated adsorption capacity reached to 725.61 mg/g and removal effect of Cr(VI)was significantly improved.(4)Mg/Al/Cr(III)layered metal hydroxide(Mg/Al/Cr(III)-LDH)was prepared using laboratory wastewater containing Cr(III),and the calcined Mg/Al/Cr(III)-LDH(Mg/Al/Cr(III)-LDO)was applied to remove Cr(VI)in laboratory wastewater.The present work simultaneously treated Cr(III)and Cr(VI)pollution by preparationadsorption technology of Mg/Al/Cr(III)-LDH.The physicochemical properties of the materials were analyzed in combination with X-ray diffraction,Fourier transform spectrum,Thermo gravimetric/differential thermal analysis N2 adsorption-desorption,Pore size of distribution curves and SEM.Mg/Al/Cr(III)-LDH was more preferable while the molar ratio of Mg(II):Al(III):Cr(III)was 10:4:1,reaction temperature was 45 ?C,aging time was 24 h.The optimal absorption condition of Cr(VI)was as follows,pH values was 8~9,solid-liquid ratio was 1:250,meanwhile,the whole process reacted at room temperature for 80 min.The maximum adsorption capacity of Mg/Al/Cr(III)-LDO for Cr(VI)was 237.80 mg/g.In this paper,the prepared Mg/Al-LDH,Mg/Al-Cr(VI)-LDH,Mg/Al/Fe(II)-LDH and Mg/Al/Cr(III)-LDH could successfully remove chromium in laboratory wastewater,and had been successfully applied in the actual laboratory wastewater treatment.The remaining concentration of chromium after treatment was in line with Chinese National Integrated Wastewater Discharge Standard(GB 8978-1996).The study provided a theoretical guidance and technical support for treating laboratory wastewater of chromium pollution.This study also provided a reference for the treatment of other chromium-containing wastewater.