Application Of Oxygenous Collector In Low Rank Coal Flotation

With the improvement of mechanization of coal mining and preparation,the yield of fine coal slime increases considerably.Generally,low rank coals including long frame coal,non-caking coal et al are utilized as thermal coal and flotation is not usually setted in their concentration process.This is mainly because there are a large amount of oxygen-containing functional groups on the surface of low rank coals,which can make them low hydrophobic capacities and then hard to float,leading to high economic cost.Actually,the contradiction between increasing yield of coal slime and its current treatment has become more and more serious,and it is badly in need of promoting industrialization of low rank coal flotation.As we can know,to find the appropriate collectors for low rank coal flotation is the most feasible method for its industrialization.Therefore,in this investigation,coal slime from a low rank coal dressing plant of Shenhua Shendong was studied.The properties of coal sample were analysised comprehensively and flotation tests using different special collectors were conducted.Meanwhile,effects of collectors on low rank coal flotation behavior were also analysised,which has a great significance in development of new efficient collectors.The ash content of coal slime used in this study is 26.20% approximately and the domain particle size is <0.045 mm with the yield of 68.97%.There is a large content of middle-density particles,which indicates that liberation degree of this sample is low.And the main gangue minerals in coal sample are quartz,kaolin and a few of clinochlore.On the other hand,there are a large amount of oxygen-containing functional groups such as C-O,C=O and O=C-O on coal surface,and the contact angle of coal sample is as low as 60.01°.In conclusion,low rank coals have poor flotability.Compared with alkane collectors,polar collectors can improve low rank coal flotation considerably.To be more specific,the improvement of low rank coal flotation by collectors containing different polar groups cannot also be identical.It can get a better flotation results in the presence of carboxylic acid at a low dosage.However,this kind of collector may lead to high ash content of concentrates.As for alcohol collectors,the length of carbon chain can have a significant impact on combustible matter recovery.Within 12 carbon atoms,carbon chains of collector have an important effect on ash content of concentrates.In terms of ketone collectors,short carbon chain can have higher flotation activity than long carbon chain collectors,but easy to make concentrates high ash content.Aldehydes with short carbon chain like pentanal have a high collectivity.However,long chain collectors such as lauric aldehyde and n-hexadecanal can make recovery decrease dramatically.As we can know from the calculations of flotation data,the values of collectivity and selectivity of alkane collectors are all low.Carboxylic acid collectors and ketone collectors can all present higher collectivity and selectivity,but meanwhile changes of carbon chain have some effects on their properties.Alcohol collectors with short chain such as n-amyl alcohol and n-caprylic alcohol have better collectivity.However,long chain collectors such as dodecanol and cetanol present low collectivity and selectivity.As for aldehydes collectors,the length of carbon chain can have a significant influence on collectivity and selectivity.From the point of HLB analysis,Carboxylic acid collectors have the highest inorganic values and alcohol collectors come second.With increase of carbon atoms,the HLB values of collectors decrease and then collectors will also be more hydrophobic.Contact angles of coal sample are all improved after collectors treatment.Specifically,contact angles of coal sample after alkane collectors treatment are 2.50-5.00o higher than that without treatment.However,the contact angles after carboxylic acid collectors treatment can be improved by 7.50o above.Alcohol collectors with short chain can enchance contact angle of coal by 8.00o or above,but long chain collectors can only make contact angle improve about 5.00o.As for ketone collectors,contact angles of coal sample after their treatment are all low except in the case of octanone(about 7.00o improvement).The contact angle after octyl aldehyde treatment can be enhanced about 10.00o.However,under the long chain collectors treatment,contact angles of coal can only be improved about 5.00o.Furthermore,from the FTIR analysis of coal sample after collectors treatment,polar groups in collectors can interact with-OH on coal surface by bonding interaction and then hydrophilic area on coal surface will decrease.Therefore,hydrophobicity of coal surface can be strengthed and better flotation results can be got.In addition,alcohols,ketones,aldehydes can still be adsorbed on the non-polar area of coal surface.