Study On Sintering System Of Sludge Brick Andits Performance And Environmental Safety

With the rapid development of climate change and social economy,the shortage of fresh water and the discharge of a large number of industrial and domestic wastewater have become prominent resource and environmental problems.Sewage treatment and reuse is one of the important ways to solve water pollution and supplement water resources.The continuous construction of a large number of sewage plants or the transformation of old sewage plants to improve the treatment scale has led to a sharp increase in the annual sludge output.However,due to the long-term existence of the "heavy water and light sludge" phenomenon,the sludge treatment and disposal has not been improved simultaneously with the sewage treatment,and the effective solution of the sludge treatment and disposal problem has become an urgent practical need.The key to solving the problem of sludge is to realize the "reduction,stabilization,innocuity and recycling" of sludge,in which the technology and application of sludge recycling are particularly emphasized.In this paper,taking Shenyang municipal sludge as an example,the feasibility of the operation process and product application of the sintered brick made of sludge mixed with coal gangue and shale materials is discussed by means of experimental research.The best sintering system was determined by testing and evaluating raw materials and optimizing the proportion of mixed materials by orthogonal test.On this basis,the impact of sludge addition on brick performance was evaluated,and the environmental safety of brick samples was evaluated by heavy metal acetic acid leaching method.The purpose is to provide scientific basis for resource utilization of sludge fired brick in Shenyang or similar areas.The main conclusions are as follows:(1)The No.3 combination in the orthogonal test is the best sintering system,that is,the sludge addition is 5%,the sintering temperature is 1050 ℃,and the sintering time is 9hours.At this time,the burning loss rate is 16.25%,the volume shrinkage rate is 1.84%,the water absorption rate is 12.29%,and the compressive strength is 20.4 MPa.The compressive performance of the sample brick reaches the MU20 strength grade in the standard of GB 5101-2003 Sintered Common Bricks.(2)The burning loss rate of sintered brick is greatly affected by the amount of sludge added,followed by the sintering time,and the sintering temperature is the least affected;The biggest factor affecting the shrinkage of sintered brick is sintering temperature,followed by sludge addition and sintering time;For water absorption and compressive strength,the biggest factor is sludge addition,followed by sintering temperature,and the smallest factor is sintering time.(3)The water absorption and porosity of sludge increased from 0% to 20%;From the perspective of compressive strength,when the sludge addition amount is 0%,5%,10% and15%,the sintered bricks are higher than MU10 grade.When the sludge addition amount is5%,the average compressive strength is better than MU15 grade,indicating that the effect of mixing with coal gangue and shale is optimal when the sludge addition amount is 5%.When the amount of sludge added exceeds 20%,the compressive strength of sintered brick is lower than 10 MPa.The grade cannot meet the factory requirements.(4)The addition of sludge is conducive to improving the weathering resistance of sintered bricks.After 15 freeze-thaw tests,the sintered bricks with 0% sludge addition appear corner drop;Some sintered bricks have frostbite on the edges;When the amount of sludge added is 20%,the sintered bricks appear cracking,and the sintered bricks with 5%-15% sludge added have no cracks.(5)The order of heavy metal leaching concentration Zn> Cu> Ni> As> Cr> Pb> Cd>Hg.The leaching concentration of heavy metals from 0-15% sludge addition is relatively stable.When the sludge addition reaches 20%,the release rate of Zn and Cd increases greatly.However,the sintered bricks with sludge addition between 0-20%,sintering temperature of 1050 ℃ and sintering time of 9 h are safe for the environment.