Research On Purification Of Low-grade Diatomite And Aperture Adjustment

China is rich in diatomite resources,ranking the second place in the world.Nonetheless,China is relatively poor in high quality diatomite resources.Utilization of the low-grade diatomite is becoming a key issue demanding prompt solution,since high quality diatomite is declining because of increasing exploitation.Low-grade diatomite generally contains a certain amount of gangue minerals,such as clay minerals,quartz,feldspar and so on.Effective methods should be developed to liberate these gangue minerals,in order to concentrate diatom.In this paper,for low-grade diatomite from Linjiang,Jilin province,purification effect and separation mechanism were studied by scrubbing,acid leaching,roasting and flotation.meanwhile,investigation of particle size control by hydrothermal treatment,high-pressured and hydrothermal treatment,and roasting was conducted to reveal the mechanism of particle size control of diatomite.The study on characteristics of mineralogy indicates that low-grade diatomite from Linjiang,Jilin was three-grade diatomite.The main gangue minerals were albite and quartz.Coscinodiscus was the main diatom,with small amount of Melosira and Stephanodiscus.The particle size of row ore was fine,with the fraction of-0.023 mm accounting for more than 87%.Crubbing,acid leaching and roasting method were used to purify the low grade diatomite.The results show that using the scrub-acid leaching-roasting purification process,under the conditions that scrub concentration of 25%,scrub time of 30 min,the settling time of 0.5 min,roasting time of 1.5 h,and roasting temperature is not higher than 600 ℃,the concentration grade of SiO2 increased,although the decreasing of Al2O3 and Fe2O3 was unremarkable,especially the grade of Al2O3 was still high.In this study,flotation was used to purify the low grade diatiomite.The results of diatomite,quartz,feldspar single mineral flotation tests showed that when using laurylamine as collector,pH value within 5.5～10.5,laurylamine dosage of 40 mg/L,the recovery rate difference between diatomite and albite or quartz can be 93.5%and 95.25%,respectively.It is helpful to realize the separation of diatomite and albite,quartz by flotation.On the basis of single mineral tests,taking the three-grade diatomite from Linjiang,Jilin province as flotation purification research object,investigations on the pulp pH adjustment agent type,pulp pH value,disperse agent type,dispersing agent,temperature of the pulp,capture cash agent dosage and flotation process were conducted.SiO2 were of grade 79.39%and 79.38%,Al2O3 of grade 4.92%and 5.04%would be obtained,with recovery rate of 45.98%and 45.00%,if in the once corse and twice process using NaOH as a pH adjusting agent,keeping pulp temperature of 40 ℃,using sodium pyrophosphate and sodium tripolyphosphate as dispersant,employing dosage of 300 g/t and 450 g/t,keeping pulp pH of 9.0 and 10.0,and DDA dosage of 550 g/t.The organic matter in the diatomite was removed after roasting,and the grade of SiO2 was increased to 84.38%and 83.97%,respectively.Results of FTIR,Zeta potential,AFM,MS and extended DLVO theoretical calculation show that the adsorptions of DDA have occurred on all the surfaces of diatomite feldspar,quartz.Amount of DDA may be adsorbed on the albite,quartz surface,leading to significant change of the surface zeta potential of albite and quartz.On the contrary,few of DDA was adsorbed on diatomite surface,that the surface zeta potential of diatomite changes a little,correspondingly.The results of AFM are consistent with the results of the MS.The results show that the DDA selectively adsorbs on the edge of holes existing on the surface of diatomite,while it can adsorb freely on the surfaces of feldspar and quartz no matter the surfaces.In summary,due to the different adsorbing characteristics of DDA on the surface of diatomite,albite and quartz,the hydrophobicity difference of the surface between diatomite and albite,quartz become larger,provides the basis for the separation of diatomite and albite,quartz.AFM is used to test the force among diatomite,feldspar and quartz under the dodecylamine system,combined with chemical analysis of dodecylamine solution and extended DLVO theoretical calculation.The results show that the interaction laurylamine and albite,quartz in aqueous solution is relatively large.Under the twelve amine system,the interaction between diatomite and albite,quartz is small.Under the dodecylamine system,when taking the pH value of 4.0,5.5,9.0,with dodecylamine taking the form of ions and dimmers,which is conducive to interaction among diatomite,feldspar and quartz,AFM detected out the fact that diatomite has smaller force with feldspar and quartz,promot:ing the separation of objective mineral and gangue minerals,which is consistent with the results of flotation purification experiment.The pore size of the diatomite was controlled by hydrothermal reaction,high-pressured and hydrothermal treatment,calcination.The results show that using silicate and sodium hydroxide as aperture adjustment,and setting the reaction temperature as 90 ℃ and 50 ℃ respectively,setting the reaction time as 2.5 h and 0.5 h,respectively,as well as stirring speed as 400 r/min,the pore size of diatomite is well controlled by hydrothermal reaction.The pore size of diatomite is 2.60 nm and 7.53 nm,respectively.The results also show that using silicate and sodium hydroxide as aperture adjustment,and setting the reaction temperature as 140 ℃ and 220 ℃ respectively,setting the reaction time as 1.5 h and 2.5 h,respectively,as well as stirring speed as 600 r/min and 400 r/min,respectively,the pore size of diatomite is well controlled by high-pressured and hydrothermal treatment.The pore size of diatomite is 2.21 nm and 2.93 nm,respectively.When the calcination temperature was 400 ℃ and the calcination time was 90min,the organic matter of diatomite removed by roasting,the internal and external channels of diatomite can be clear.The pore size of diatomite is 2.67 nm.Diatomite aperture control mechanism show that a large number of silicon hydroxyl groups exist in the pores of diatomite,silicic acid gel can form Si-O bonds with the diatom surface silanols,and three-dimensional network structure inside the pores of diatomite which can separate the channel,thereby increasing the diatomite specific surface area and make average pore radius of diatomite decreases.The suitable concentration of NaOH could have a certain dissolution effect on the shell of diatoms under the high temperature.After dissolution of the hole wall,the pore size of diatomite is increasing,and the specific surface area of diatomite is decreasing.This paper have reference value to studies on realizing the high efficient,energy saving and shortprocess of diatomite purification,lay the foundation for the mechanism analysis of the flotation purification of diatomite,and provide reference for research on regulation of diatomite aperture.