Study On Purification Of Anthracite And Its Tribological Properties As Lubricant Additive

Anthracite,the raw ore grade is generally 70-90%,is the largest degree of coalification in all coal species.Because anthracite is often closely combined with other gangues and distributed in clay,it is difficult to be used directly.At present,anthracite is mainly used as energy fuel after simple treatment,which is not only low utilization rate but also harmful to environmental protection.In this paper,the purification and new application of anthracite in Tianhu mountain,Fujian Province are studied.After mineralogical characterization of raw ore,the two-step flotation-acid leaching method was used to purify the raw ore,and then the purified product was used as lubricating oil additive to prepare the composite lubricating oil by ultrasonic and ball milling in situ and to test the tribological properties.The main results are as follows:First,the flotation purification technology of anthracite ore with fixed carbon content of 76.42%was studied.The primary ore mainly exists in block form,and the particle size is mainly distributed between 500 and 1000?m;the main mineral impurities are quartz,mica and chlorite,etc.;it mainly contains elements such as C?O?Si and Al;and the degree of defect is large(I_D\I_G=1.70).In order to meet the flotation requirements,the original ore was first ball-milled for 6 h.This process could not only make the bulk into lamellar,but also not destroy the microcrystalline structure of the ore.The primary and secondary factors and optimal flotation conditions were determined by orthogonal test:flotation concentration>amount of foaming agent>amount of trapping agent>inhibitor addition amount;the flotation concentration was 60 g/L,amount of foaming agent was 160 g/L,amount of trapping agent was 260 g/L,amount of inhibitor was 40 mg/L.Under the optimum flotation conditions,the fixed carbon content of the raw ore was increased to 93.17%by a coarse separation and six times selection,and the carbon recovery rate was 85.03%.Then,the flotation concentrate was chemically purified.After analyzing the physical properties of concentrate,the test scheme of mixed acid soaking was formulated,and the influence of mixed acid volume ratio,reaction time and reaction temperature on the acid leaching process was investigated by controlling variable method.The results show that when the volume ratio of hydrofluoric acid to sulfuric acid is 3:2 and the reaction time is 180 min,the reaction temperature is 50?,the fixed carbon content can be increased to 95.98%and the ash content reduced to0.14%.However,the physical properties of acid-immersed concentrates indicate that the acid-immersed process may affect the microcrystalline structure of flotation concentrates and reduce the degree of concentrate defects(ID/IG=1.26).Finally,lubricating oil with the surfactant-coated anthracite was prepared in situ by ultrasonic and ball milling treatment with acid-immersed concentrate and non-ionic surfactant span80 as lubricating oil additive and dispersion auxiliaries,respectively.Then,the effects of additive concentration,operating load,temperature and rotational speed on the tribological properties of lubricating oil were investigated.The results showed that the average friction coefficient,wear scar diameter and wear volume of the surfactant-coated anthracite oil were reduced by 45.39%,60.13%and95.95%,respectively,compared with the base oil at 150 N.And the lubricating oil has also stable tribological properties at varying loads,temperatures and rotational speeds.The anti-wear and anti-friction effect of anthracite could be attributed to the fact that the sheet and well-dispersed anthracite could easily enter the friction pair and deposit on the surface,forming protective film,which can bear the load and repair the defects.