Research On Regulation Technology And Environmental Protection Function Of Bentonite Composite Binder For Casting

Based on bentonite,pulverized coal and pulverized coal substitute material application defects in casting and the damage to the environment.Combining the development trend of green sand casting,the bentonite samples collected from Wuhu,Anhui province(marked as WH),Xinyang,Henan province(marked as XY)and Santai,Sichuan province(marked as ST).In addition,using microcrystalline graphite(marked as G),coal gasification slag(marked as M)and"carbon"from titanium slag(marked as T)as pulverized coal substitute material.The application effect of bentonite composite binder in foundry was studied,and the mechanism of the bentonite composite adhesive was revealed.The mineralogical properties of bentonite samples from three mining areas showed that the methylene blue consumption of the bentonite samples from the three mining areas could meet the national standard(GBT 20973-2007“Bentonite”)the first-class quality requirements of the bentonite for foundry.And the wet compressive strength indexes of the XY and ST samples met the second-level quality requirements of the national standard,while the WH sample met the national standard three-level quality requirements.Among the three bentonite samples,the casting property of ST sample was the worst.The three samples were sodium modified by the method of extrusion sodium modification with Na₂CO₃ as sodium agent,and the optimum sodium process conditions of the three samples were obtained.Under optimized sodium conditions,the wet compressive strength index of XY-G sample met the first-class quality requirements of the national standard(GBT 20973-2007“bentonite”).And the wet compressive strength of WH-G and ST-G samples met the second-class quality requirements.The study of physical and chemical properties of samples G,M and T showed that the ash content of sample G was the lowest,while the fixed carbon content was the highest.Samples G,M,T and MF,after 750?C high temperature treatment,the change of phase were small,but when the temperature rose to 1000?C,only sample G remained stable.In addition,the pyrolysis gases of samples G,M and T produced in 1000?C were less phenols and some polycyclic aromatic hydrocarbons(PAHs)than those of sample MF.In addition,the total amount of harmful gases produced by samples G,M and T were10.09%,5.82%and 6.99%of that of sample MF,respectively.The three-order simplex barycenter design method was used to optimize the combination of the selected pulverized coal substitute materials.Finally,the optimal ratio of pulverized coal substitute materials was determined as G:T=4:1(m:m).The ash content of sample GT was 19.57%,the volatile content was 4.16%,the fixed carbon content was 76.24%,the thermal expansion rate at 1200?C was 1.442%,and the high temperature thermal stability was better than sample MF.According to the comprehensive performance of each bentonite sample,the sodium bentonite samples were mixed and finally determined that the optimal mixture ratio of bentonite was WH-G:XY-G=1:1(m:m).And the wet compressive strength of the sample can reach 117.69 k Pa when the addition amount was 8%(mass ratio of quartz sand).The study of complex was carried out of the mixed bentonite sample(HB)and pulverized coal substitute material.Finally,the optimal ratio of bentonite composite binder was determined as HB:GT=8:5(m:m),and the wet compressive strength of the sample was 133.93 k Pa(sample MF was 126.95 k Pa).With bentonite composite binder for sand mixing molding,casting aluminum castings,the surface of the casting was smooth.And after repeated use for five times,the casting quality was still at a high level,the wet compressive strength of sand mixing sample was still 152.78 k Pa.Activation tests of waste foundry sand were carried out by alkali excitation method,and the effects of activator types and excitation time on the activation effect were explored.The results showed that Na₂Si O₃ was better than Na OH,and when the concentration of Na₂Si O₃ was 3.0 mol/L,the wet compressive strength of the sample was 39.17 k Pa.The wet compressive strength of the sample could reach 41.35 k Pa after24 h of excitation when Na₂Si O₃ was used as base activator.