Effect Of Compound Filter Reagent On The Dewatering Performance Of Flotation Clean Coal And Its Mechanism

Coal is the largest fossil energy used in China,and efficient sorting of coal is the first step to achieve its clean and efficient utilization.At present,most of the coal preparation plants in China are focus on wet preparation,and the high moisture of the washed product will bring many adverse effects on the downstream industry,among which,the slow filtration speed of flotation clean coal coal and the high moisture of the filter cake are particularly prominent problems.In this thesis,a compound filtration reagent system of surfactant and CPAM is constructed by virtue of the filtration dehydration test of flotation clean coal.The surface tension of the filtrate,the interfacial properties,the interaction forces of the particle surface,the floc size evolution in the slurry and the pore structure of the filter cake were investigated by using a fully automatic tensiometer,contact angle meter,zeta potential analyser,FBRM-PVM and low field NMR analyser.The study was carried out to explain the mechanism of filtration and dewatering of flotation clean coal enhanced by the compound filter reagent.The sample selected for the filtration test was a difficult to dewater flotation concentrate.Both the flocculants and surfactants were used to promote the dewatering process of the flotation concentrate,from which CS,CD and CB compound filter aids,those aids were selected and combined.Filtration rate of 827.77 m L/s·m2at optimum dosage,which is 20.27%and 69.10%higher than that of CPAM and DTAB with the same dosage only;CB-type compound filter aid maximally reduces the filter cake moisture,which is 22.96%with the best dosage,which is 3.61%and 6.57%lower than that of CPAM and Brij L23 with the same dosage only.The compound filter reagent changes the particle zeta potential and hydrophobicity in the slurry conditioning process,which reduces the energy barrier of the interaction force between particles and reduces the repulsive force,promoting the formation and size of flocs in the coal slurry;while promoting an increase in the porosity and a looser structure of the filter cake in the filtration stage;the increase in pore space and the reduction in the surface tension of the filtrate lead to a reduction in the capillary water pressure difference in the Laplace-Young equation,promoting the increase in pores and the reduction in surface tension of the filtrate lead to a reduction in the capillary water pressure.The test results show that:the surface tension of the filtrate is significantly reduced after the addition of the compound filter reagent,the contact angle of the flotation clean coal is reduced,and the absolute value of the zeta potential of the particles is reduced;the energy barrier of the total interaction energy of the particles is reduced by the EDLVO theory calculation,and it is easier to attract each other across the energy barrier and promote the flocculation of the particles,and the CB type filter reagent has the best effect in reducing the energy barrier;the addition of the compound filter reagent effectively promotes.The addition of compound filtering reagent effectively promotes the increase of small floc size,and this phenomenon is related to the reduction of interparticle interaction repulsion by the compound filtering reagent,and the best effect of CB type filter reagent in promoting the increase of floc size;the compound filtering reagent increases the porosity of medium and large pores inside the filter cake,resulting in a more loose structure of the filter cake,and the content of free water also increases,which jointly promotes the removal of water from the filter cake,and the porosity of the filter cake is the largest after the addition of CB type filter reagent.The filtration speed of the flotation clean coal was improved with the addition of the compound filter reagent in acidic solution and high concentration of Al³⁺solution;alkaline solution,Na⁺,Ca²⁺solution and low concentration of Al³⁺solution had a negative effect on the increase of filtration speed of the flotation clean coal with the compound filter reagent;acidic,alkaline solutions and different concentrations of Na⁺,Ca²⁺and Al³⁺solutions had a negative effect on the reduction of cake moisture with the compound filter reagent;among the three filter reagents,CD-type filter reagent is more alkaline resistant,while CB-type filter reagent is more acidic and salt resistant.There are 47 pictures,7 tables and 99 references in this thesis.