The Synthesised And Strengthened Of The Poly-aluminum-ferric-silicate-chloride In Coking Wastewater Treatment

Coking wastewater is a highly concentrated organic wastewater,which is usually generated in the process of coke-making,coal gas purification,and chemical refining in coking plants.Due to the presence of refractory and inhibitory contaminants,the effluents from biological treatment system still contain a relatively high concentration of non-biodegradable organic pollutants,and most of them are dissolved organics.The traditional coagulant is not effective to remove these bio-refarctory organics,and it often requires a large coagulant dosage.As a result,the effluent from the systems can not meet the discharge regulations.Poly-silicic-metal coagulant is a new type of inorganic polymer flocculatants.It has a good charge neutralization,adsorption bridging and net capturing ability,and has been regarded as a potential coagulant fororganics removal.Moreover,poly-silicic-metal coagulant can be synthesized from a wide raw material sources such as fly ash,coal gangue,metal tailing and other silicate solid waste.This will broaden the reuse of these solid wastes and reduce the corresponding environmental issues during their disposal.However,the previous studies were focused on the coagulation performance in terms of turbidity,color and COD.The investigation on the organic removal by this kind of coagulant is very rare.In addition,the optimal formula and dosage were diffrerent from case to case in the literature,which is largely owing to the different raw materials and wastewaters.This paper aims to prepare three composite coagulant poly-aluminum-silicatechloride(PASiC),poly-ferric-silicate-chloride(PFSiC)and poly-aluminum-ferricsilicate-chloride(PAFSiC)first and apply them in tertiary-treatment for coking wastewater.The floc properties were also studied to evaluate the sludge settling ability of the three coagulants.Based on the above analysis,the best coagulant(PAFSiC)was selected for the bio-treated coking wastewater.Then,PAFSiC was synthesized and optimization from coal gangue.The effect of Al/Fe/Si,pH and dosage on the structure and coagulation perfromance were investigated.In addition,Zeta potential and floc morphology analysis were conducted to understand the coagulation mechanisms.Finally,the effect of silicon dose on morphology structure,coagulantion performance and floc properties of PAFSiC from coal gangue was investigatedsysmatically.This study will provide a theoretical foundation on the preparation of suitable poly-silicic metal coagulant for coking wastewater.The main conclusions are as follow:(1)Based on jar-test results: PASiC,PFSiC has apparent difference in removing the organic matter from wastewater.Three-dimensional fluorescence analysis shows PASiC was effective in removing the fulvic acids and microbial metabolites but its effect on humic acids was weak.However,PFSiC exhibited an apparently removal of humic acids but it did not work on fulvic acids and microbial metabolites.GC-MS results showed that: PASiC was effective on removal of polymeric aromatic hydrocarbons(PAHs),long-chain alkane(LASs),aldehydes,carboxylic acids and esters(ACEs),and nitrogen,oxygen and sulfide-containing heterocyclic compounds(NOSs),as reflected by the relative content of these substances before and after coagulation.PFSiC only showed specific interactions with ACEs which containing-CO-,-COOH,and-COO-functional groups.PAFSiC has a broad range of organic matter removal ability,which combines the advantages of the PASiC and PFSiC.Its coagulation performance is the best with color,UV254 and DOC removal reached83.8%,59.9% and 59.9% respectively.Furthermorethe flocs of PFSiC have the largest floc size and most compact structure,implying a good settling ability in the following sedimention process.The flocs of PASi C were apparently smaller and looser than PFSiCs.However,the resultant flocs of PAFSiC have slightly lower floc size and strength than PFSiC,but they have more branch-like units with less agglomeration in the structure.The structure is believed to be favorable to capture,adsorb and enmesh the bio-refractory organics from the bio-treated coking wastewater.(2)PAFSiC was synthesized from coal gangue,and optimum constitute of PAFSiC is Al/Fe(3:1),(Al+Fe)/Si(13:1),and optimal pH range is 6-9.Flocculation experiments showed that color,turbidity,UV254,COD,DOC removal of 78%,88.2%,50.1%,54.3%,34.5% were achieved at PAFSiC dosage of 125 mg/L.And the COD of effluent after flocculation was 66.8 mg/L,which is below the discharge limit in the regulation “The coking chemical industrial pollutant discharge standard”(GB16171-2012).Except for the charge neutralization effect,the well chain-net structure of PAFSiC provides the strong adsorption bridging and net capturing ability in theflocculation process.(3)Silicon content not only has influences on the formation of Si-O-Al and Si-O-Fe functional groups,but also on the PAFSiC morphology structure.At the high silicon content,the PAFSiC mainly presents the laminated structure and has a large number of irregular particle.The particle gradually dissappear and has the tendency of integration to form net chain structure at low silicon content(10:1 and 13:1),.Jar-test results showed that too high or too low silicon content would lead to deterioated coagulantion performance.The best removal efficiency color,UV254 was at(Al+Fe)/Si=13:1,and the best removal efficiency of DOC was 10:1 or 13:1.Silicon content also has a significant influence on the floc structure.With the decrease of silicon content,the average particle size of flocs was decreasing.However,the floc fractal dimension and strength factor was increased in the first,and peaked at the(Al+Fe)/Si=10:1 and(Al+Fe)/Si=13:1,and decreased greatly.The results indicate that the flocs density and hydraulic impact resistance is still strong at 10:1 and 13:1 in spite of their reduced floc size.