Preparation Of Oxidized Kerosene And Its Mechanism In Oxidized Coal Flotation

The difference in surface properties between raw coal and oxidized coal is the cause of difficulty in flotation of oxidized coal.After the coal is oxidized,a large amount of oxygen-containing functional groups appear on the surface,which makes the surface of the oxidized coal increase in polarity,resulted in the deterioration of hydrophobicity;and flotation effect.The use of a conventional collector has a problem that the amount of the agent used is high and the flotation effect is poor.Therefore,this paper studies the difference in surface properties before and after oxidation of coal,finds the types and proportions of difficult-to-float surface groups;According to the mechanism that the collector with the oxygen-containing groups can improve poor floation performance of the oxidized coal surface,and changes through catalytic oxidation.The proportion of polar oxygen-containing groups in the kerosene has been changed,which increases its compatibility with the difficult-to-float groups on the surface of the oxidized coal,and improves the surface floatability of the floating coal,thereby achieving efficient and economical purposes.The high-ash and easily oxidized raw coal from Liangdu Coal Mine was oxidized in a 100?ventilated drying oven for 48 h to prepare artificial oxidized coal slurry.The FTIR,XPS,contact angle,Zeta potential,and surface wetting heat of raw coal and oxidized coal were measured to characterize the change of surface properties before and after oxidation of coal.Tests show that after low temperature oxidation of raw coal,the surface of the coal-CH₃,-CH₂ functional groups are partially oxidized by air to oxygen-containing functional groups such as C=O,C-O,-COOH,etc.,wherein the C-O group:-COOH group is about 4:1.After flotation of this oxidized coal,it was found that the yield of clean coal was only 44.30%,indicating that the generated oxidized functional groups are the origin of difficulty in floating.Thereafter,three collectors with the same hydrophobic carbon chain and different hydrophilic oxygen-containing groups are formulated into model collectors in different proportions,which can be obtained by flotation test of the oxidized coal.It has been found that when the model collector was used,the yield of clean coal is increased by 20.86%,the recovery rate of combustibles is increased by 24.91%,compared to the useofdodecaneone.Themodelcollectorincludes dodecane:dodecanol:dodecanoic acid,whose ratio is 2:6.4:1.6.In this case,the best flotation effect was obtained.Subsequently,according to the proportion of mixed collector,the oxidized kerosene was prepared by using manganese naphthenate as catalyst and air oxidation.The optimal oxidation conditions of kerosene were determined by flotation experiments:oxidation temperature 150?,catalyst concentration 0.1%,air flow rate 200 mL/min,oxidation time12 h.The use of this oxidized kerosene as a collector,compared with the use of kerosene,the yield of clean coal of oxidized coal slurry increased by 23.72%,the recovery rate of combustibles increased by 28.72%,and the improvement index of flotation improved by 7.9%.After characterization by FTIR and GC-MS,it was found that after the catalytic oxidation reaction of kerosene with air,the methyl group and alkane in kerosene were partially oxidized to oxygen-containing groups such as alcohol,acid,ester,aldehyde and ether,and the obtained oxidized kerosene was alcohol:the acid ratio is about 4:1,which is consistent with the alcohol/acid ratio of the model collector.After measuring the Zeta potential and the wetting heat,it can be seen that the oxidized kerosene can reduce the absolute value of the Zeta potential and reduce the heat of wetting on the surface of the oxidized coal.The above results indicate that the oxygen-containing groups in the collector may be adsorbed on the surface of the oxidized coal at a specific site,and it is highly likely that the alcohol-in the collector attcahes to the-CO bond on the surface of the oxidized coal and the acid adsorbs to-COOH bond on the surface of the oxidized coal..In order to verify the hypothesis,a coal sample with low temperature oxidation for 12 hours was selected,and the degree of oxidation of the coal sample was determined by XPS.It was found that the ratio of-CO and-COOH group on the surface of the oxidized coal was about 2:1,a model collector was prepared to float it.After the test,it was found that a best flotation result was obtained when the alcohol:acid was 2:1.Finally,the interaction mechanism of the collector and the oxidized coal is as follows:the polar portion of the collector can be selectively adsorbed on the polar surface of the oxidized coal,wherein the alcohol in the collector tends to react with the-CO bond on the surface of the oxidized coal.Acid tends to bond with the-COOH bond on the surface of the oxidized coal,causing the non-polar portion to be exposed on the surface of the coal to form a non-polar surface,thereby reducing the absolute value of Zeta potential and the wetting of the surface of the oxidized coal.As a result the hydrophobicity and floatability of the oxidized coal increase.