Preparation Of Ceramsite Based On Loess And Its Application In The Initial Runoff

Loess is widely distributed in Northwest China.As a kind of adsorbent,because of its abundant reserves and low price,loess has broad application prospects in the field of water treatment.However,in the form of powder,loess is easy to lose and clogged when use it as adsorbent,and difficult to regenerate.Coal gangue is the waste produced in the process of coal mining,which is usually accumulated around the mine.It not only occupies land,but also pollutes the environment.Meanwhile,it should not be neglected that coal gangue is also a natural adsorbent,which can be effectively utilized as a resource to turn waste into treasure.For the purpose of effective utilization of resources,the ceramsite was prepared by loess and coal gangue to treat the initial runoff of rainwater in this dissertation.Taking 1 hour water absorption,mud content and hydrochloric acid solubility as the performance indexes of ceramsite,the effects of the ratio of auxiliary materials（bentonite,sodium silicate and calcium carbonate）,sintering system,particle size and ratio of coal gangue were investigated respectively.The optimum technological parameters of ceramsite preparation were determined by single factor test and orthogonal test.The ceramsite prepared under the optimum technological conditions were characterized and tested.The ceramsites were used as filter filler to study the treatment effeciency of initial runoff before and after film-forming.The main research contents and results are as follows:（1）The chemical composition of loess and gangue was determined by EDS,and compared them with Riley’s three-phase diagram.It’s necessary to add some accessories to prepare the ceramsite.That bentonite,sodium silicate and calcium carbonate was finally determined to be the accessories by subsequent experiments.（2）According to the national standard"Water Treatment Artificial Ceramsite Filter Material"（CJ/T 299-2008）,taking the 1 hour water absorption,mud content and hydrochloric acid solubility rate as performance indicators,combined with the treatment effect of loess-based ceramsite on the initial runoff,the technological conditions were preliminarily determined by single factor test,and the orthogonal test was designed to determine the optimum technogical condtion.And the optimum technological conditions were as follows:m_bentonite accounted for 10%of the raw materials,msodium silicate accounted for 15%of the raw materials,mcalcium carbonate accounted for 5%of the raw materials.The preheating temperature was 400℃,the preheating time was 5 min,the roasting temperature was 950℃,the roasting time was10 min,the particle size of coal gangue was less than 0.25 mm,m_loess:m_{coal gangue} was2:1.（3）The performances of ceramsite prepared under the optimum technological conditions are as follows:water absorption rate of 1 hour was 24.82%,sludge content was 0.42%,hydrochloric acid solubility was 0.81%,density was 1.64 g/cm³,cylindrical compressive strength was 9.07 MPa,specific surface area was 6.26×104 cm²/g.（4）The ceramsite were characterized and the results showed that the specific surface area of loess-based ceramsite was larger than other ceramsite,it was rough and ravine,its internal pore was abundant to be used as adsorption filler.The surface of ceramsite was negatively charged,so it was easy to absorb positive ions.Because of microorganisms were generally positively charged and hydrophilic,it was easy to load microorganisms when the ceramsites were used as biological filter material.Therefore,it was considered that loess-based ceramsite was suitable for water treatment filler.（5）The ceramsites prepared under the optimum conditions were filled into the experimental column to treat the initial runoff,and the effects of thydraulic retention time and filter material thickness on treatment efficiency were studied.The results showed that when the hydraulic retention time was 8 h,as the hydraulic load was 1.75m³/[m³（filter material）·d],the retention and adsorption of the system were maximized,and the removal rates of turbidity,COD,ammonia nitrogen,TN and TP were 98.81%,45.23%,50.25%,54.52%and 67.12%,respectively.When runoff passed through the whole packing layer by upward flow,the 200 mm ceramsite at the bottom could complete most of the interception and adsorption.（6）When loess-based ceramsites were used as biological filter,the removal efficiency of COD,ammonia nitrogen and TN after film-forming was significantly improved.After stable operation,the turbidity of effluent was 5.35±1.0 NTU,the removal rate was 97.50±0.5%;the COD concentration of effluent was 56.00±1.9 mg/L,the removal rate was 70.53±1.0%;the ammonia nitrogen concentration of effluent was2.60±0.2 mg/L,the removal rate was 73.47±2.0%;the effluent TN concentration was4.80±0.34 mg/L,the removal rate was 71.68±2.0%;the effluent TP concentration was0.72±0.05 mg/L,the removal rate was 69.20±2.0%.After stable operation,all water quality indicators except TP meet the first-class A effluent requirement of Pollutant Discharge Standard for Urban Sewage Treatment Plant（GB 18918-2002）.