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Research On The Adsorption Of Cd2+ In Wastewater By Modified Excess Sludge

Posted on:2015-11-24Degree:MasterType:Thesis
Country:ChinaCandidate:Z LuFull Text:PDF
GTID:2181330467979279Subject:Environmental Science and Engineering
Abstract/Summary:PDF Full Text Request
As a new technology for heavy metal wastewater treatment, bio-absorptionmethod has the advantages of extensive material sources, low cost, large adsorptioncapacity, quick absorption rates, good treatment efficiency, easy operation and easyregeneration. It’s own a quite broad application prospect in heavy metal wastewatertreatment.This subject is an adsorption experiment research on Cd2+in heavy mentalwastewater and the adsorbent is excess sludge from municipal sewage plant modifiedwith NaOH and H2O2. The main content includes analysis on the physical andchemical properties of excess sludge; discussion about changes that happened toshape and properties before and after the sludge’s modification; studying on aspectsabout the adsorption characteristics, desorption and regeneration conditions; thekinetics, isotherms and thermodynamics studies are also involved; besides, itdiscussed the mechanism of adsorption Cd2+.The experimental results show that: the modified excess sludge’s apparentmorphology structure have changes obviously, BET is increased from13.602m2/g to16.845m2/g; Zeta potential become more negative and is conducive to the adsorptionof cationic; The adsorption process is about60min achieves adsorption equilibrium,when the pH is6.0, at25℃, the initial concentration is40mg/L,and the adsorbentconcentration is2.0g/L, the maximum adsorption capacity is15.76mg/g, it is60.82%higher than that of unmodified. The inhibition effect of adsorption by four kinds ofcationic is in the following order: Ca2+>Mg2+>K+>Na+, and the competitioncoexisting ions is in the order of Cu2+>Zn2+>Pb2+. The adsorption process conforms tothe Lagergren pseudo-second-order kinetic model, the fitting coefficient R2>0.999;The fit of the Langmuir isotherm model is superior to the Freundlich isothermaladsorption model, its linear correlation coefficient R2is0.999, belongs to themonolayer adsorption. Thermodynamic analysis results is△G0<0,△S0>0,△H0>0,it indicates that the adsorption process is spontaneous and endothermic, and theraising temperature can promote the adsorption process. With1.0mol/L HCl asdesorption reagent, three times in the desorption process, the adsorption capacity ofregeneration adsorbents respectively are96.51%,91.18%,83.63%of the originalmodified adsorbent. XRD spectrum found no obvious crystal substances generated inadsorption process. The result of XRF indicate that the content of Na, Mg, Ca in modified adsorbent is changed after the adsorption, they decreased from0.248%,0.542%,1.25%to0.129%,0.506%,0.888%respectively. Also, the content of Cd isincreased to0.505%,which did not detected before the adsorption.27%of theadsorption process is complete by ion exchange, the modified adsorbent release1.135mg Ca2+and0.235mg Mg2+per gram. FTIR analysis shows that migration happenedafter adsorption in the wavenumber of3432cm-1、2927cm-1、2856cm-1、1654cm-1、1541cm-1、1406cm-1、1083cm-1、1033cm-1, even characteristic peak weakened ordisappeared, these phenomena indicate that the complexing of the correspondinghydroxyl, carboxyl, amide groups with the adsorbed Cd2+is happened, whichcompleted the adsorption of Cd ions.
Keywords/Search Tags:excess sludge, biosorption, modification, Cd, mechanism
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