Effect Of Adding Surfactants In Grinding Process On Lignite Flotation

Lignite resource is abundant in our country. Most of the lignite is used as fuel for electricity generation at present. Because the lignite cannot be effectively separated, it causes a variety of environmental problems. People gradually pay attention to research on effective methods to lignite separation. Especially for Fine lignite, it is difficult to reach high recovery employing conventional flotation processes because of its weak floatability. This thesis takes Xishi lignite as an example to find out the difficult-to-float characteristic of lignite. The strategies, applying surfactants and combining them with grinding, for improving flotation of lignite are proposed. Their improvement mechanisms of joint action are also researched by advanced instrumental analysis methods. The main conclusions are as follows:(1) Difficult-to-float characteristic of lignite is investigated based on physicochemical characterization. FTIR, XPS, SEM and contact angle measurements are applied for physicochemical characterization of difficult-to-float characteristic. The surface of lignite shows strong hydrophilicity is attributed to that there are a large number of oxygen containing groups, cracks and ravines on it. And moreover, a large amount of mineral covers on the lignite surface or fills in the ravines. As a result, lignite is difficult to float using conventional flotation processes. In order to improve the fotability of lignite, not only the oxygen containing groups content but also the mineralcontent on the lignite surface should be reduced.(2) Flotability contrast of lignite after being modified with different agents and the mechanism is investigated. Floatation experiments of lignite which was modified with three agents indicate that floatability of lignite after span80 modified can be enhanced. Span formula and XPS results show that due to differences in the length and structure of the non-polar side, the activation performance of span80 is better, which makes span80 easier to adsorb on the lignite surface, so the hydrophobicity and flotability of lignite are both improved significantly. However, high ash mineral on lignite surface is also covered slightly after span80 modified. Span 80 has good modification while weak selective effect, which leads to high ash content in concentration.(3) Impacts of flotation conditions on lignite flotation are investigated. Minerals in the ravines can be stripped under vigorous stirring impeller speeds. When the total mixing time keeps constant, prolonging pre-wetting time can improve the flotation until it reaches to 5 minutes. In addition, adding flotation reagents in the flotation process will hinder this phenomenon. When the impeller speeds is less than 1196 r/min, mainly due to the impact of flotation agitation, the combustible matter recovery of concentration increases quickly. That is because that the diameter of bubble becomes smaller with increasing of impeller speeds. When the impeller speeds is more than 1196 r/min, a joint influence of flotation agitation and mixing agitation leads to entrainment and balance point movement of fine minerals filling and stripping. As a result, concentration ash content increases while combustible matter recovery decreases.(4) Effect of adding surfactants in grinding process on lignite flotation and its mechanism is studied. Since the lignite surface is covered by minerals, clean coal has high ash content and low combustible matter recovery. Grinding pretreatment can improve the floatability of coarse particles and the selectivity of fine particles. Grinding can make fine minerals strip from coarse coal to dissociate minerals from coal. And adequately dissociation results in lower ash content of concentration.. In addition, the lignite surface will contact and adsorb with agents more easily without the impact of minerals. The selectivity of fine particles increases because that grinding promotes adsorption between lignite and agents.In summary, adding surfactants in grinding process is presented based on the study of difficult-to-float characteristic of lignite for improving floatability. Grinding is applied to make surface minerals dissociated to improve separation effect and adding surfactants to perfect floatability. It provides an effective process method for flotation deashing and hydrophobicity improvement.