Promoting Effects Of Wettability Modification On Oxidized Coal Flotation

Oxidized coal containing abundance of surface oxygen-containing functional groups decreases the coal hydrophobicity and floatability which makes flotation of oxidized coal difficult to achieve using the common flotation processes. Adsorption of surfactants through polar interactions of the hydrophilic groups with oxygenated sites on coal surface could increase hydrophobicity and improve floatability of oxidized coal. The hydrophilic mineral will turn to hydrophobic because surfactants also adsorb on mineral surface while interacting with organic components of coal. This leads both clean coal yield and ash increase substantially. This paper proposed utilizing difference in adsorption strength on mineral and organic matter and hydrothermal method in proper operating conditions to selectively desorb surfactants form coal surface. Surfactants adsorbed on organic surface were retained and adsorbed on mineral surface were desorbed, thus the hydrophobicity of organic matter were enhanced with the adsorption of surfactants, wettability differences between organic and mineral surfaces were expanded and the purpose of increasing floatability and effective segregation of oxidized coal was achieved.In this paper, oxidized coal was prepared using ash coal form Wangpingmine, Datong coal mine group by artificial oxidation method and pure minerals of kaolin, quartz and calcium carbonate were used. Three kinds of surfactants(CTAB, SDS and TX-100) were chosen for adsorption pretreatment on oxidized coal and pure minerals respectively. Adsorption characteristics of surfactants on oxidized coal and pure mineral surface were analyzed with FT-IR spectra and its effects on flotation result were investigated. Desorption status of surfactants on oxidized coal, kaolin, quartz and calcium carbonate under 80℃ hydrothermal condition were studied. After hydrothermal treatment, clean coal yield and cleans ash changes of oxidized coal treated with surfactants were discussed.Main conclusions of the study are as follows:(1) Adsorbed amount of surfactants on oxidized coal surface increased with surfactant concentration. After adsorbing surfactants, hydrophobicity of oxidized coal increased and the floatability improved. But concentrations of different surfactants should be strictly controlled: concentration range of CTAB:0~300mg/L, SDS: 0~100mg/L and TX-100: 0~150mg/L.(2) CTAB, SDS and TX-100 also adsorbed on minerals while adsorbed on organic matters of coal which decreased hydrophilicity of minerals. Therefore,clean coal yield increased accompanied with increasing cleans ash.(3) Hydrothermal treatments of oxidized coal(organic matter), kaolin,quartz and calcium carbonate which were treated with different concentration surfactants in advance, were performed in thermostatic water bath at 80℃。The results showed that saturated alkyl content on oxidized coal surface increasedand the hydrophobicity was enhanced. While surfactants adsorbed on mineral surface were desorbed and thus the hydrophilicity was enhanced.(4) Hydrothermal pretreatment before flotation operation could selectively desorb surfactants(CTAB, SDS and TX-100) on minerals surface of oxidized coal, thus decreased cleans ash and improve clean coal recovery.