Study On The Preparation And Surface Modification Of A Novel Ceramsite And Its Utilization In Simulated Wastewater

Solid wastes?SW?has been widespread concerned by the international society because of its widely source distribution,great harm to the environment,complex component,variety and treatment difficulty.Reduction,harmlessness and reuse are three main principles in the SW treatment.Reclamation of SW not only can reduce the consumption of non-renewable natural resources,but also can improve the utilization of SW,realizing harmonic development of society,environment and economy.Ceramsite is widely used in water treatment because of its excellent functions,including large specific surface area,developed pore structure and lower heavy metal leaching toxicity.With the necessary additives,ceramsite was obtained from SW by high-temperature sintering process,which not only can achieve reutilization of SW,but also can promote sustainable development of ceramsite industry.In this research,ceramsite was preparation by high-temperature sintering process with dewatered sewage sludge?DSS?,coal fly ash?CFA?and river sediment as the raw materials,its physical properties were characterized.Then ceramsite was applied to degrade simulated wastewater before surface-modified.The main conclusions of this study were summarized as follows:1.The preferred conditions for the preparation of ceramsite by high-temperature process were:the mass ratio of DSS,CFA and river sediment was 5:1:4,the dosage of CaCO₃ and Na2 Si O3 were5% per 100 g mixture,preheated at 400 ? for 20 min and then sintered at 1150 ? for 5 min.The investigated physical properties of ceramsite,included breaking and wear rate?0.2%?,solubility inhydrochloric acid?0.0%?,silt carrying capacity?0.2%?,void fraction?71.1%?and BET specific surface area?0.73× 104 cm2/g?,met with the China's industrial standard of CJ/T 299-2008 and the concentration of heavy metals in the lixivium was lower than the threshold of GB 5085.3-2007.During the sintering process,the sintering behavior of ceramsite could be well described by the3-order polynomial fitting curve,with high correlation coefficient values?R2> 0.999?,the cut-off temperature was 700 ?.The expansion performance of ceramsite was a dynamic equilibrium model of contraction firstly and then expansion.2.Removal efficiency of MB from aqueous solution by ceramsite fixed-bed column combined with high-temperature calcination for regeneration were studied.The results showed that under the column operating conditions of MB initial concentration of 5 mg/L,ceramsite particle size of 0.5 mm and flow rate of 1.0 m L/min,the adsorption behavior of MB on ceramsite fixed-bed column followed the Thomas model closely,R2= 0.980.Furthermore,at 15% and 50%breakthrough for MB,the breakthrough data are agreed well with the BDST model,and R2> 0.99.The optimal regeneration conditions for exhausted ceramsite were as follows: regeneration temperature and time were 600 ? and 60 min,respectively.After regeneration,the regeneration lost rate of ceramsite was only 1.35%.Compared with the regeneration lost rate of activated carbon?approximately 5¹0%?,the regeneration lost rate of ceramsite was still below 3% even after recycled 4 times,suggesting that ceramsite exhibits strong regeneration capacity.3.The ceramsite coated with nano-Cu2 O photo-catalyst material was synthesized via liquid-phase reduction and dipcoating method,respectively.Under experimental conditions the initial concentration was 15 mg/L,pH was 3,reaction temperature was 25 ? and photocatalyst dosage was 0.5 g,the photocatalytic degradation rate of MB reached 93.31% after stirring 95 min?adsorbed for 20 min and Xe light irradiated for 75 min?,suggesting that this photo-catalyst material exhibits strong photocatalytic activity.One of the main reasons is that the ceramsite coated with nano-Cu2 O material possesses many outstanding characteristics,such as higher BET specific surface area,larger pore size and stronger visible-light adsorption capacity.Under visible-light irradiation,the photocatalytic degradation process of MB by ceramsite coated with nano-Cu2 O was found to follow the pseudo-first order kinetics model,with high correlation coefficient values?R2> 0.95?.Phenols,esters and amines were main degradation intermediates for MB photocatalytic degradation and the desired products were SO₄^2-and NO₃^-.The degradation pathways of MB were proposed during the photocatalytic degradation process,containing at least two different ways that occurred simultaneously.4.After 1.0 mol/L NaCl solution modified,the BET specific surface area and pore size of ceramsite were increased 1.27 and 1.4 times,respectively.More importantly,the content of Na element in the surface of ceramsite increased from 2.85 to 6.18?wt%?.When the NH₄⁺-N initialconcentration was 100 mg/L and temperature was 328 K,the equilibrium adsorption capacity of modified ceramsite was 2.49 mg/g after stirred 180 min,which was 1.79 times as high as that of cereamsite,indicating that after modified by 1.0 mol/L NaCl solution,the adsorption capacity of modified ceramsite was improved significantly.The Langmuir and Freundlich isotherm models can well describe the adsorption equilibrium of NH₄⁺-N on modified ceramsite in the whole experimental conditions?R2> 0.95?.On the contrary,the adsorption equilibrium of NH₄⁺-N on ceramsite can only well follow the Freundlich isotherm model?R2> 0.95?.The pseudo-first order model can be batter described the adsorption of NH₄⁺-N onto modified ceramsite in all investigated initial concentrations than the pseudo-second order model.The intra-particle diffusion model can be employed to describe the adsorption of NH₄⁺-N on modified ceramsite in the whole experimental conditions,with good correlation?R2> 0.97?.NH⁺4-N adsorption on modified ceramsite is a physisorption process,with entropy increase,properly raised of temperature will be helpful for the adsorption.5.Compared with other removal processes,the ceramsite coated with nano-Mg?OH?₂coupled with air stripping process had the highest NH⁺4-N removal efficiency from aqueous solution,after stripping for 150 min,the removal rate was more than 86%,no matter what acidic?pH=3?,neutral?pH=7?or alkaline?pH=11?conditions.Under the experimental conditions of initial pH was 7,air flow rate was 0.8 L/min,initial concentration was 450 mg/L and reaction temperature was 328 K,the removal of NH₄⁺-N by the combined process could be fitted by the general-first order kinetics model,R2> 0.97.The reason is mainly because of the fact that in the presences of H+ or NH⁺4,Mg?OH?₂ is unstable and hydrolyzes easily in aqueous solution.The major hydrolyzed product is OH-,which may be promote air stripping through neutralization reaction with H+.In conclusion,ceramsite,satisfy the requirements of relevant standards,could be prepared by high-temperature method from SW.During the process of simulated wastewater treatment,ceramsite can be used as fixed-bed column filler,adsorbent or supporter.This research maybe plays an examplary role in the practicing the new concept of disposal waste with waste in water treatment.