Promotion Of Reductant Agents On The Flotation Of Oxidized/Low-Rank Coal

With the decreasing reserves of high quality coal resources in China,it is imperative to improve the quality of oxidized/low-rank coal and comprehensively utilize it.The oxygen-containing groups on the surface of coal are easy to combine with water to form hydrogen bonds,which is the main reason for the difficulty of flotation and low flotation efficiency of oxidized/low-rank coal.Many scholars can improve the coal surface hydrophobicity and flotation efficiency by adjusting reagents or pretreatment of coal,which can improve the difficulty of oxidized/low-rank coal floatation.Reducing agents have certain applications in mineral flotation.For oxidized/low-rank coal,reducing agents may interact with some oxygen-containing functional groups on the coal surface to change the surface properties and improve the flotation effect.In this experiment,the coal from Guanlingshan,Majialiang and Manlailiang were selected as the research objects.The degree of coalification of the three coal was analyzed by proximate and ultimate analysis.The mineral composition and surface morphology of the coal were analyzed by XRD,BET and SEM.The forms and contents of surface functional groups in coal samples were analyzed by FT-IR and XPS.Because of the composition and surface properties are very different,the flotation effect of these three coal samples is different.Guanlingshan coal is oxidized coal with high metamorphism degree,and has a lot of folds,which affect the flotation efficiency.Majialiang coal has medium metamorphism,and high oxidation degree,with a large number of minerals attached,and has many cracks resulting in low flotation efficiency.Manlailiang coal has low metamorphism degree,and serious surface oxidation with many pores resulting in difficult flotation.According to the different surface properties of coal samples,the reducing agent,were tried for pretreatment in flotation tests,and the reducing agent with better effect was found to explore the promotion effect of oxidized/low-rank coal flotation.The effects of Na₂SO₃,Na NO₂,Na₂S₂O₃,KI,Sn Cl₂,Fe Cl₂ and FeSO₄ on flotation were studied by using clean coal yield,combustible recovery and ash content as evaluation indexes.The pretreatment conditions of Na NO₂,Fe Cl₂ and FeSO₄ were also studied,including dosage,pretreatment time,pretreatment p H and so on.The flotation results show that the dosage of reagent has the greatest influence on the results,the pretreatment time should not be too long,and the p H has little influence.Na NO₂works best and is universal.The optimal conditions of Guanlingshan coal flotation pretreatment are Na NO₂ dosage 2000 g/t,pretreatment time 3 min,no adjustment of p H.The optimal conditions for flotation pretreatment of Majialiang coal are Na NO₂ dosage 2000 g/t,pretreatment time 5 min,and p H.The optimal conditions of Manlailiang flotation pretreatment were Na NO₂ dosage 2500 g/t,pretreatment time 5 min,p H=7,and the flotation test results were the best.The optimum pretreatment conditions such as dosage,pretreatment time and p H of FeSO₄were determined.The optimal conditions for the flotation pretreatment of Guanlingshan coal are as follows:dosage of FeSO₄ 1000 g/t,pretreatment time 3 min and alkaline environment.The flotation pretreatment of Majialiang coal has a negative effect.The optimal flotation pretreatment conditions of Manlailiang coal were FeSO₄ dosage 1500 g/t and 3 min pretreatment time.There are abundant pores and folds on the surface of coal samples,and the specific surface area of coal particles is large.The chemical ions reach the surface of coal particles,act on the electrical layer on the surface of coal,compress the Stern electrical layer on the surface of coal,and affect the electrical properties of the surface of coal samples.Moreover,the surface of oxidized/low-rank coal is rich in oxygen-containing functional groups,such as hydroxyl,etc.Nitrite reacts with them to reduce the content of oxygen-containing groups,improve surface hydrophilicity,and effectively improve flotation efficiency.The decrease of coal surface electronegativity and increase of hydrophobicity are the result of chemical action.