| Textile dyeing sludge is a mixture of biological and chemical sludge from the industrial wastewater treatment plant which containing a variety of heavy metals,complex organic matter,high moisture content and the compressive strength is low.Textile dyeing sludge will be harmful to the environment if it is treated and disposed inappropriately.In this paper,muddy analysis was conducted at first.Various factors on the geotechnical properties of the cured block,heavy metals and toxic organic matter leaching characteristics were studied on the basis of the combinations of "cement,attapulgite," "cement,fly ash,attapulgite," "typical working condition Comparision"which were considered with dyeing sludge characteristics and common cement and fly ash cement curing system.In addition,the suitable additive combinations were chosen to study the leaching kinetic characteristics of metal(copper)and toxic organic matter(benzene)in the different simulated circumstance of underground water,acid rain and acid solution secreted by plants respectively.At last,technical and economic analysis of the optimized program were carried onassuming the daily treatment of 500t textile dyeing sludge with 85%moisture.Main conclusions were as followed.(1)Al,Fe and Mg were the dominant elements in the textile sludge used in the experiment,which occupied more than one thousandth of the dry sludge.Heavy metals such as Cu,Zn,Cr,Pb and Mn were also detected by ICP.Main phases of Cu and Zn in textile sludge were exchangable phase(F1),bound to carbonates(F2)and bound to Fe-Mn oxides(F3).While organic-bound(F4)and residual fractions(F5)were not dected.Infrared spectrum results showed that textile sludge contained carboxyl group,aromatic structure,carbonyl group and aliphatic acid.Results of leaching test indicated that the leaching concentrations of Cu,Zn and Pb were 2.11 mg/L,1.91 mg/L and 1.14 mg/L respectively.The concentration of benzene and methylbenzene leachated from the sludge were 56.9 mg/L and 18.3 mg/L,which were 55 and 17 times higher than the concertrations in criteria of Chinese dangerous wastes control standard.(2)The moisture of the solidified blocks decreased with time when textils dyeing sludge was solidified by cement and attapulgite(Designed by Software Design expert,mixture design,D-optional,the mass ratio of the addtives were set as follows:sludge 0.1-0.8;cement 0.1-0.8;attapulgite 0-0.3).The moisture of the solidified blocks were below 60%after 7 d and the moisture of the samples were about 10%after 28 d.The unconfined compressive strength(UCS)of solidified blocks increased with time.Afer 7 d,more than 50 kPa of UCS was achevied by each sample,which met the requirement of landfilling.Some of the solidified blocks’ UCS were higher than 2 MPa which met the requirement for soil bricks and paving.The influence degree of different additives on the moisture was cement>attapulgite>fly ash which was verifed by comparing cement,fly ash and attapulgite as additives to solidify the textile dyeing sludge(mass ratio of cement to sludge were 0.2,0.4,0.6;mass ratio of fly ash to sludge were 0.1,0.3,0.5;mass ratio of attapulgite to sludge were 0.05,0.1,0.2).Moreover,cement,attapulgite and fly ash were beneficial to improve the UCS of the blocks.Resluts of typical condition experiment showed that attapulgtie led to lower moisture,higher UCS and lower pH than fly ash.Ettringite and Calsium Silicate Hydrate gel(CSH)were confirmed by denser surface,needle-like and honeycomb-like structures,atom composition and crystals detected by XRD.Calcite,quartz,tricalcium silicate and mullite were main crystals in the solidification process.Fly ash could improve the hydration reaction of cement.(3)The concentrations of Cu,Zn and Pb in the leachate from the solidified blocks at 1 day,7 days and 28 days were 0.04-1.6 mg/L,0.03-0.71 mg/L and 0.04-0.19 mg/L respectively when cement and attapulgite were usedas solidifaction agents(same setting mass ratio as(2)),and the con concentrations were far below the criteria of hazardous wastes.Moreover,increase the ratio of cement and attpulgite could decrease the relative metal concentration in the leachate.Qudratic model was an effective method to describe the relationship between the metal concentration and the mass ratio of cement and attapulgite.Immbolization of Cu was controlled by attapulgtie adsorbtion,encapsulation of cement successively.While the reaction of calcium silicates with Zn,adsorbtion of attapulgite and sealing of Zn by cement hydrations were the successive dominate power of Zn solidification.When cement,fly ash and attapulgite were added to solidify the textile dyeing sludge(same setting mass ratio as(2)),Cu,Zn and Pb leaching concentration were 0.3～1.3 mg/L,0.01-0.058 mg/L and 0.2～0.4 mg/L.,The influence order on Cu,Zn and Pb were attapulgite>cement>fly ash;fly ash>attapulgite=cement and fly ash>attapulgite>cement respectively.Resluts of typical condition experiment showed that attapulgite was better to reduce Cu,Zn and Pb leaching concentration than fly ash.F4 and F5 phase of Cu were increased after solidification and attapulgite promoted heavy metal into residual state.In additon,increasing cement mass ratio led Cu into F4 phase.F4 and F5 phase of Zn increased after solidification and attapulgite stimulated Zn into stable phases.Furthermore,cement and attapulgite were appropriate solidify agents to make Cu and Zn into more stable phases.(4)The concentrations of COD,benzene and methylbenzen in the leachate from the solidified blocks were 106-986 mg/L,0.2-1.35 mg/L,0.17-2.47 mg/L when cement and attapulgite were used as solidifaction agents after 7 d.Cement and attapulgite could be uesd to decrease the COD,benzene and methylbenzene of the leachate.Quadratic model were suitable to express the relationship between the pollutants concentration of the leachate and the addtives.When cement,attapulgite and fly were added for sludge solidify,the minimum COD was 429.32 mg/L,and the relative benzene and methylbenzene concentration were 0.4-1.7 mg/L and 0.9-4.3 mg/L.Orthogonal method experiment showed that the influence order on the concerntrations of COD,benzene and methlbenze in leachate were fly ash>cement>attapulgite,Cement>fly ash>attapulgite and cement>fly ash>attapulgite.Especially,when sludge,cement,fly ash and attapulgite msas ratio were set to 0.512,0.308,0.154 and 0.026,the concentration of benzene and methylbenzene of the solidified blocks after 7 d met the requirement of nonhazdrous control criteria in china.Resluts of typical condition experiment showed that attapulgite was better than fly ash in decreasing COD,benzene and methlbenze leaching concentration.(5)The leaching kinetic experiment under the circumstance of deionized water,sulfuric-nitric acid and oxalic acid were carried on when sludge,cement,fly ash and attapulgite were added in the mass ratio of 0.512,0.308,0.154 and 0.026 after 7 d.Leaching of Cu was stronger by oxalic acid than sulfuric acid and nitric acid water.The leaching of Cu were divided into two stages.Both of the two stages were first order kinetic founctions,and the second stage turned out to be slower than the first stage.The benzene leaching period were also divided into two stages.While the first stage was second order kinetic function and the second stage were in line with logarithmic distribution.(6)According to the daily processing of 85%moisture content and dyeing sludge 500 t,a curing harmless program was used for equipment selection,technical and economic calculation,namely,the mass ratio of sludge,cement,fly ash and attapullgite was set to 0.513、0.308.0.154 and 0.026.Process economical analysis results showed that fixed asset investment was at least 3.35 millon yuan and operation cost was 286.7 yuan/t sludge. |
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