Adsorption And Immobilization Of Pb,Cu By Modified Alum Water Treatment Residuals(Al-WTRs)

With rapid development of urbanization,the number and scale of water treatment plants are increasing,accompanied by much water supply,however,the amounts of water treatment residuals?WTRs?also increased.A large number of WTRs bring some pressure to environment,hence,finding appropriate handling methods for WTRs is particularly important.WTRs are mainly composed of flocculant?aluminum salt or iron salt?,clay particles and a small amount organic matter,now,WTRs have been used as constructed wetland substrate,pollutant adsorbent,soil ameliorant due to their properties,however,there are few studies on the modification of WTRs.This study was based on Al-WTRs as raw materials which produced from water treatment plant of Yangling,Shaanxi,Pb and Cu as target pollutant,KMnO₄,FeCl₂·4H₂O and K₂HPO₄·3H₂O as modification reagent,to discuss Pb²⁺and Cu²⁺adsorption by M-Al-WTRs obtained under different modification conditions?Fe/Mn ratio,Fe/Mn total concentration,K₂HPO₄·3H₂O added proportion and temperature of water bath?,and chose the modification conditions with better adsorption effect.Fe/Mn-Al-WTRs and P-Al-WTRs were prepared with chosed modification conditions,and their characterization were analyzed with BET-N₂,SEM-EDS,XRD and FTIR.Additionally,batch adsorption experiments were conducted to investigate the effects of pH,adsorption time,initial mass concentration of Pb²⁺and Cu²⁺,temperature and ion strength on the adsorption properties of Fe/Mn-Al-WTRs and P-Al-WTRs.Pot experiment was carried out with Tongguan heavy metals polluted soil as background soil,ryegrass as indicator plant.The effect of different addition ratios?0.5%,1.5%and 2.5%?of Al-WTRs,Fe/Mn-Al-WTRs and P-Al-WTRs on soil pH,organic matter,cation exchange capacity and Pb,Cu content of DTPA was discussed.After a month of ryegrass planted,compared the effect of the three additives on ryegrass biomass,Pb and Cu concentration of shoots and roots.The main results and conclusions are listed:?1?The better modification condictions of KMnO₄,FeCl₂·4H₂O for Al-WTRs were:Fe/Mn ratio with 7:3,Fe/Mn total concentration with 0.7 mol/L,bath temperature with 40?.Specific surface area of Fe/Mn-Al-WTRs prepared with chosed conditions were 100 m²/g,which is more than 11 times the surface of Al-WTRs.The scanning electron microscope showed that the surface of Fe/Mn-Al-WTRs was rough and loaded with many particles,indicating that Fe and Mn had been successfully loaded on Al-WTR.XRD showed that amorphous was also remained in Fe/Mn-Al-WTRs.The infrared spectrum analysis showed that after modification with iron and manganese oxides,-OH vibration peak was slightly shifted and significantly enhanced,and while Fe-O and Mn-O vibration peaks were appeared.The adsorption amounts of Fe/Mn-Al-WTRs for Pb²⁺and Cu²⁺increased significantly with pH increasing.At pH=5,the adsorption amounts of Fe/Mn-Al-WTRs for Pb²⁺and Cu²⁺were 67.2,20.8 mg/g,respectively,while the adsorption amounts of Al-WTRs for Pb²⁺and Cu²⁺were 32.1,12.3 mg/g.The adsorption of Fe/Mn-Al-WTRs for Pb²⁺and Cu²⁺was quickly in the first 4 h,at this time,the adsorption amounts of Pb²⁺and Cu²⁺have reached 76.9%,72.1%of equilibrium adsorption capacity respectively,and adsorption equilibrium was basically reached at 12 h.Dynamic analysis results showed that the adsorption process of Fe/Mn-Al-WTRs for Pb²⁺and Cu²⁺could be described with the pseudo-second-order kinetic model,which was chemical adsorption.Adsorption isotherm fitted Langmuir model well,which was monolayer adsorption.Additionally,the thermodynamic analysis showed that the adsorption process of Fe/Mn-Al-WTRs for Pb²⁺and Cu²⁺was spontaneous,endothermic and entropy increased.Moreover,the adsorption of Pb²⁺and Cu²⁺was hardly affected by ionic strength.?2?The better modification condictions of K₂HPO₄·3H₂O for Al-WTRs were:K₂HPO₄·3H₂O ratio with 1:10?g/mL?,bath temperature with 100?.Specific surface area of P-Al-WTRs prepared with chosed conditions were 37.9 m²/g,which is more than 3 times larger than the surface of Al-WTRs.The scanning electron microscope showed that the surface of P-Al-WTRs was loose and loaded with many particles,energy spectrum analysis indicated that P had been added to Al-WTRs.With pH increasing,adsorption amounts of P-Al-WTRs for Pb²⁺and Cu²⁺increased first and then decreased.At pH=5,the adsorption amounts of P-Al-WTRs for Pb²⁺and Cu²⁺were 42.2 and 13.8 mg/g,which was more than31.2%and 11.5%compared with Al-WTRs.The adsorption process was quickly at the first 2h,and the adsorption amounts of Pb²⁺and Cu²⁺reached 86.6%,83.4%of equilibrium adsorption capacity respectively,adsorption equilibrium was basically reached at 12 h.The adsorption effect of P-Al-WTRs for Pb²⁺and Cu²⁺increased with temperature increasing,which indicated that adsorption process was endothermic.?3?After two-months of Al-WTRs,Fe/Mn-Al-WTRs and P-Al-WTRs added to Tongguan contaminated soil,pH,CEC and OM of soil were all improved with different degree when compared with control,the Pb and Cu content of DTPA decreased.With the increase of WTRs addition,the uptake of Pb and Cu continously decreased in shoots and roots of ryegrass,when the additive amount was 2.5%,the contents of Pb,Cu in shoots and roots of ryegrass decreased 60.1%,32.4%,52.8%,44.8%in Fe/Mn-Al-WTRs;31.9%,14.5%,6.41%,17.0%in P-Al-WTRs and 7.34%,10.9%,5.94%,11.4%in Al-WTRs.In general,among the three additives,Fe/Mn-Al-WTRs have a more significant effect on immobilization Pb,Cu and reduction phytoavailability.This shudy shows that Al-WTRs could be used as effective materials to adsorb heavy metals and improve soil,and reasonable modification of Al-WTRs can improve their utilization.