Study On The Effect And Mechanism Of Surfactant On Coarse Slime Dewatering

With the progress of coal preparation methods,the independent separation and dewatering of coarse slime has been gradually realized.However,because the size of coarse slime is smaller than that of conventional tailings,even if a centrifuge is set up independently to dehydrate the coarse slime,the moisture content of the coarse slime concentrate is often higher,so that the moisture content of the total concentrate is also higher,which further affects the quality of the total concentrate and the product price,and ultimately has a negative impact on the economic benefits of the coal preparation plant.At present,chemical filter aids,including surfactants,are usually added in the process of pressure filtration dewatering of fine coal slime to reduce product moisture and improve dewatering effect,Its advantages are that it can avoid the disadvantages of traditional dehydration methods,such as complex process,environmental pollution,increased energy consumption and production costs.In this paper,polyoxyethylene?20EO?sorbitol monolaurate?Tween20?,polyoxyethylene?20EO?sorbitol monooleate?Tween80?,sorbitol tristearate?Span65?,sorbitol monooleate?Span80?,sodium dodecyl sulfate?SDS?and Cetyltrimethylammonium Bromide?CTAB?were used as filter aids in the dewatering process of coarse slimes.The dewatering effect of coarse slime on arc screen from Buertai Coal Mine?CS-1?and coarse slime fed by centrifuge from Daliuta Coal Mine?CS-2?was studied,and their filter aid mechanism was explored.Firstly,the basic properties of the two kinds of coal samples are analyzed,such as particle size composition analysis,density composition analysis,industrial analysis,element analysis,potential analysis,FTIR structure analysis and X-ray diffraction analysis,to grasp the basic properties of coal samples;Secondly,in the process of dehydration of coarse coal slime,different types of surfactants with different dosages were added to carry out dehydration comparative tests and conditions exploring tests,and the dehydration effect of coarse coal slimes under different conditions and optimum filter aid conditions were explored.The surface morphology,surface functional groups and contact angle of CSs,properties of centrifugal fluid,i.e.,surface tension and the adsorption of surfactants by coal samples after dehydration under different conditions were characterized.The main conclusions are as follows:?1?The CS-1 of coarse slime used in the experiment was dominated by+1 mm particle size,which accounted for 47.79%of the total particle size and 1.3-1.4 g/cm as the dominant density grade.The density grade accounted for 26.07%of the total density grade.The content of moisture(M_ad),ash(A_ad),volatile matter(V_ad)and fixed carbon(FC_ad)were 6.22%,21.13%,37.30%and 35%respectively.The CS-2 was dominated by 1-0.5 mm particle size,accounting for 32.61%of the total particle size.The density grade was mainly 1.3-1.4 g/cm,accounting for 28.37%of the total density grade.The contents of moisture(M_ad),ash(A_ad),volatile matter(V_ad)and fixed carbon(FC_ad)were6.69%,9.21%,35.61%and 48.49%respectively.Fixed carbon content of CS-1 and CS-2 differed the most,35.35%and 48.49%respectively,followed by ash content,21.13%and 9.21%respectively.?2?The effect of different surfactants on the dewatering effect of CSs was studied by dewatering contrast test.The results show that the dewatering effect of CSs can be improved by adding surfactant in the dewatering process,and with the increase of surfactant dosage,the precipitation rate of coarse slime increases first and then tends to be stable,which is much higher than that of blank sample.Except Span65,the other five surfactants?including Tween20,Tween80,Span80,SDS,CTAB?have remarkable filter aid effects.Tween20 can make the precipitation rates of CS-1 and CS-2 reach15.59%and 15.89%respectively;Tween80 can make the precipitation rates of CS-1and CS-2 reach 12.85%and 17.80%respectively;Span65 can make the precipitation rates of CS-1 and CS-2 reach 4.23%and 7.07%respectively;Span80 can make the precipitation rates of CS-1 and CS-2 reach 11.75%and 14.18%respectively;SDS can make the precipitation rates of CS-1 and CS-2 reach the highest.CTAB can make the precipitation rates of CS-1 and CS-2 reach 15.74%and 12.13%respectively.?3?By investigating the effects of three surfactants?Tween20?SDS?CTAB?on the dewatering effect of CS-2 under different experimental conditions?including the speed of mixing,the time of mixing,the centrifugal factor,the centrifugal time and the dosage of the agent?,the results showed that the centrifugal factor,the centrifugal time and the dosage of the surfactant had a significant effect on the centrifugal dewatering effect of CS-2,and the mixing time had a significant effect on the centrifugal dewatering effect.,and the speed of agitation had little effect on the dehydration effect of CS-2.The optimum test conditions of the three surfactants for CS-2 filtration aid were as follows:?1?Tween 20:600 r/min mixing speed,8 min mixing time,110centrifugal factor,4 min centrifugation time and 0.6 kg/t dosage.Under the optimum experimental conditions,the moisture content of CS-2 dehydrated with Tween 20 was15.87%,and the precipitation rate was 21.08%compared with the blank sample;?2?SDS:mixing speed 600 r/min,mixing time 8 min,centrifugal factor 110,centrifugal time 4min,dosage 0.4 kg/t.Under the optimum experimental conditions,the moisture content of CS-2 dehydrated with SDS was 15.75%,and the precipitation rate was 21.68%compared with the blank sample;?3?CTAB:mixing speed 600 r/min,mixing time 8min,centrifugal factor 110,centrifugal time 4 min,dosage 0.8 kg/t.Under the optimum experimental conditions,the moisture content of CS-2 dehydrated with CTAB was16.72%,which was 16.86%higher than that of the blank sample.?4?By characterizing the adsorption amount of surfactants on coarse slime under different dosages of surfactants,the properties of coal samples before and after surfactant modification and the properties of centrifugal fluid,the following conclusions are drawn:Firstly,all six surfactants can modify the two kinds of coarse coal slime in different degrees,including changing its surface morphology,reducing the superfine minerals adhering to the surface of coarse coal slime,reducing the hydrophilic oxygen functional groups on the surface of coarse coal slime,and increasing the contact angle of coarse coal slime.Secondly,surfactants can reduce the surface tension of centrifugal fluid,thus promoting the removal of centrifugal fluid.The adsorption capacity of CS-2 on surfactant increases with the increase of dosage of surfactant,but when the dosage reaches a certain value,the adsorption capacity no longer increases significantly.This paper includes 26 figures,11 tables and 103 references.