Study On Flocculation Mechanism And Selectivity Flocculation Of Ultra-fine Coal And Minerals In Coal Waste Slurry Using Microbial Flocculant

At present,inorganic flocculants and polymer flocculants are widely applied in coal waste slurry treatment in coal preparation plants,which are harmful to people live and environment.Microbial flocculant,as a non-toxic and non-secondary pollution substance,shows a great importance to human health and environment protection and also has a great and far-reaching significance in coal waste slurry treatment.In this study,a strain producing bioflocculant with high flocculating activity on coal waste slurry was screened out from soil samples.It was identified as Azotobacter chroococcum by analyzing its colony character,morphological and physiological characteristics using the partial 16 S rDNA sequencing method.The flocculating active substances were distributed in the extracellular metabolites.The best culture conditions for bacteria are: sucrose as carbon source,the initial pH,culture temperature,the shaking speed and the culture time are 6.3,30℃,150 r/min and 4 days,respectively.The number of bacteria can reach 7.1×108 per milliliter by flat colony counting method at the best conditions of culture.The flocculant production is at its highest when the flowing conditions are met: sucrose as carbon source,the initial pH 8.1 and the incubation time were 4 days;the flocculant production can be reach to 172 mg/L.With coal waste slurry as the research objects,the effects of the dosage of flocculant GSY-9,the concentration of coal slurry,pH value,the type of metal ions and the amount of coagulant CaCl2 on the flocculation rate of coal waste slurry were studied by single factor analysis.The flocculation effect of flocculant GSY-9 with and without CTAB on coal waste slurry,organic matter in coal and minerals associated coal slime were investigated.The results show that flocculation rate can be up to 90.23% of bioflocculant when the following conditions are met: slime water concentration 30 g/L and a flocculant concentration of 80 mg/L,pH 2.2.Ca²⁺ is the best coagulant aid of GSY-9;the flocculation rate is 92.54% when the dosage of Ca²⁺ is 0.5 g/250 mL.Flocculation experiment of the organic matter and minerals in coal indicates that the order of flocculent effect for bioflocculant GSY-9 is organic matter > kaolin > illite > quartz.The flocculating rate of quartz is remarkable improved by using CTAB with flocculant GSY-9,which increases from-25.45% to 97.07%.Compositions and flocculation characteristics of flocculant GSY-9 were investigated by many methods.Infrared spectra show there is hydroxyl,carboxyl groups and other polar groups in its molecule.Zeta potential measurement results show that flocculant GSY-9 and the particle surface of clay minerals and quartz are negatively charged.Polysacchride and protein accounted for 62.77 % and 37.23 % in the molecules of bioflocculant GSY-9,respectively.The main action forces of bioflocculant GSY-9 vary with diffierent components in coal waste slurry: the mainly acting force between bioflocculant GSY-9 and organic matter is hydrogen bond,accompanying with electrostatic and hydrophobic interaction,and multilayer adsorption can occur during this process.For the clay minerals,the main force between bioflocculant GSY-9 is hydrophobic interaction accompanying with electrostatic repulsion.The electrostatic repulsion is mainly acting force between bioflocculant GSY-9 and quartz,GSY-9 can disperse quartz.The organic matter and clays minerals in coal waste slurry first adsorb on the sites of bioflocculant GSY-9 in the process of flocculation experiment.Because of the long-chain of GSY-9,flocculant molecule interacts with each other based on bridging action to form a net to capture the suspended particles during the descent process,thus effective flocculation is completed.