| Reasonable treatment and disposal of remaining urban sludge is a problem Traditional surplus sludge treatment and disposal technologies are mainly landfill,farmland utilization,incineration and composting,with landfill as the most important method.However,due to the limitations of the site or high environmental risks,the traditional treatment methods can no longer meet the requirements of urban green development.In recent years,solid waste treatment policies have evolved from reduction to recycling,and sludge resource utilization has become an inevitable choice for solving sludge hoarding and achieving green and sustainable developmentIn this subject,municipal dehydrated sludge was used as the raw material,and calcium oxide modified dehydrated sludge was used to prepare calcium oxide-enhanced sludge-based adsorbent(CaO-SA).The mechanical strenghth,heavy metals adsrorption ability,adsrorption behavior and adsorption mechanism of CaO-SA all were studied.By exploring the influence of preparation conditions on the mechanical strength of CaO-SA and its ability to adsorb heavy metals,the best preparation conditions were determined,and the mechanism of calcium oxide modified dewatered sludge was clarified.The influence of operating conditions on Cd(Ⅱ),adsorption performance,adsorption kinetics,isothermal adsorption and adsorption thermodynamic characteristics of CaO-SA were evaluated by the static adsorption experiment.And the adsorption operating conditions were optimized by Box-behnken surface optimization method.Combining the changes of the surface morphology and physicochemical characteristics of the adsorbent before and after adsorption,the adsorption mechanism of Cd(Ⅱ)adsorption was discussed.At the same time,CaO-SA was applied to the treatment of actual mineral processing wastewater to evaluate its effect on the treatment of heavy metals in actual wastewater.The research conclusion is as follows:(1)The optimal preparation condition of CaO-SA was that the amount of calcium oxide is 5%and the drying temperature is 60℃.The saturated adsorption capacity of the prepared adsorbent was 0.73 mmol·g-1.After enhanced modification with calcium oxide,the surface morphology and physical and chemical properties of the adsorbent change as follows:the specific surface area and pore volume become larger,the carboxylic acid is deprotonated,and the calcium ion content increases.The above changes increase the adsorption sites,improve the ion exchange capacity and the ability of functional groups to bind heavy metals,and thus enhance the adsorption capacity of the adsorbent.At the same time,the use of calcium oxide causes coagulation,carbonation and Ca(OH)2 in the sludge to cement the sludge into a whole,improving the mechanical strength of CaO-SA(2)The optimization of the conditions for CaO-SA adsorption of Cd(Ⅱ)was based on the prediction model of the Box-Behnken surface optimization method,and the optimal adsorption conditions are determined as follows:adsorption time 90min,adsorbent dosage 1 g·L-1,pH For 5,the temperature was 40℃.Under this condition,CaO-SA adsorbed 5 mg·L-1 Cd(Ⅱ)simulated wastewater,and the removal rate reached 99.74%.CaO-SA had a good recycling function.In the Cd(Ⅱ)simulated wastewater,the initial concentration was 100 mg·L-1,the adsorption time was 3 h,the adsorbent dosage was 1 g·L-1,the pH was 5,the temperature was 25℃,carry out the adsorption experiment;the desorption liquid was 1.0 mol·L-1 HCl,the desorption time was 6 h,the adsorbent was added in the amount of 1 g·L-1,the temperature was 25℃,and the desorption is carried out.After three times of regeneration by adsorption and desorption,its 100 mg·L-1 Cd(Ⅱ)wastewater removal rate reached 77%.In the adsorption system,the presence of Cu(Ⅱ),Zn(Ⅱ)and Pb(Ⅱ)is not good for CaO-SA to Cd(Ⅱ),and its competitive adsorption relationship is Cu(Ⅱ)>Zn(Ⅱ)>Pb(Ⅱ)>Cd(Ⅱ).The common co-existing cations Mg(Ⅱ),K(Ⅰ)and Na(Ⅰ)have an adverse effect on the adsorption of Cd(Ⅱ)by CaO-SA(3)The process of CaO-SA adsorption of Cd(Ⅱ)conforms to the quasi-second-order kinetic model,and the adsorption equilibrium model conforms to the Langmuir adsorption isotherm model.Chemical adsorption mainly determines the reaction rate of CaO-SA for Cd(Ⅱ)adsorption.The adsorption is mainly single layer adsorption,and it is a spontaneous endothermic reaction.The main path of the adsorption process is(1)Cd(Ⅱ)and Ca(Ⅱ)in the adsorbent(Ⅱ)Adsorption on the surface of the adsorbent by ion exchange;(2)Cd(Ⅱ)chelates and complexes with the carboxyl group(COO-)and hydroxyl group(-OH)in the adsorbent for adsorption.Among them,ion exchange is the main adsorption route.(4)CaO-SA had a good adsorption effect on heavy metal ions in the actual beneficiation wastewater.The Box-Behnken surface optimization method was used to optimize the adsorption conditions of CaO-SA for the adsorption of Pb(Ⅱ)(25±mg·L-1)beneficiation wastewater,and to determine the optimal adsorption conditions:the dosage was 6 g·L-1,the temperature was 40℃,pH=11,and the adsorption time was 30 min.After the adsorption of CaO-SA under this condition,the effluent concentration of Pb(Ⅱ)is 0.093 mg·L-1,which meets the lead emission standard of "Lead and zinc industrial pollutant emission standards(GB 25466-2010)" of 0.5 mg·L-1 requirements.The results of dynamic column adsorption experiments show that under the conditions of 1 mL·min-1 for inlet and outlet flow rates,20 min of hydraulic retention time,60 mm height of adsorbent material layer,180 mm height of adsorbent liquid,and 25℃ continuous temperature.Within 85 hours of adsorption,the effluent concentration of Pb(Ⅱ)reached the requirement of 0.5 mg·L-1 for the lead discharge standard in the"Lead and Zinc Industrial Pollutant Discharge Standards(GB 25466-2010)". |
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