Purification And Comprehensive Utilization Of Low-grade Shangtianti Bentonite

There are huge reserves of bentonite deposit in Shangtianti,Henan Province,but it lacks of exploitation and utilization,and the mineral resources are seriously wasted.Based on this situation and the current development trend of bentonite products in China's industrial field,this paper systematically studied the mineralogical properties of Shangtianti bentonite,and carried out purification by self-powdering technology,preparation of activated clay by low-temperature calcination at atmospheric pressure and one-step synthesis of zeolite at atmospheric pressure.The optimum technological conditions of each method have been obtained,which can provide remarkable economic benefits for the development and utilization of bentonite in this area.The study on mineralogical properties of Shangtianti bentonite showed that the main phases of bentonite ST-B1,ST-B2 and ST-B3 were Ca-montmorillonite,and the associated impurity minerals were clinoptilolite and cristobalite;among them,ST-B1 and ST-B3 belong were low-grade bentonite with poor properties,whlie ST-B2 was medium-grade bentonite with relatively superior properties.Through self-powdering purification technology,the amount of methylene blue absorbed by ST-B1 increased from 28.93 g/100g to 34.85 g/100g,ST-B2 from 34.74g/100g to 38.55 g/100g,and ST-B3 from 25.75 g/100g to 37.99 g/100g,indicating the remarkable purification effect of this method.In the purification process,the montmorillonite enriched mainly in fine grains could be effectively separated with clinoptilolite enriched in coarse grains,but could not be separated with cristobalite.Activated clay was prepared by calcinating the raw bentonite with low-temperature at atmospheric pressure with concentrated sulfuric acid as activating agent.The optimal conditions for the preparation by ST-B1 were 20%for the mass ratio of H₂SO₄/bentonite,200? for activation temperature and 30 min for the activation time.The optimal conditions for ST-B2 were 15%for the mass ratio of H₂SO₄/bentonite,200? for the temperature and 20min for the activation time.As for ST-B3,the optimal conditions were 25%for the mass ratio of H₂SO₄/bentonite,200? for the temperature and 40 min for the activation time.The performance of the activated clay prepared under the optimal conditions met the requirements of the first-class products in HG/T 2569-2007 Activated Clay.Zeolite was synthesized with low-grade raw bentonite by one-step synthesis at atmospheric pressure.The optimum conditions for synthesizing 4A zeolite with ST-B1 were Na/Si=5,Si/Al=0.9,with the reaction time of 15 h and temperature of 70?;the optimal condition for synthesizing 4A zeolite with ST-B3 were Na/Si=4,Si/Al=0.8,with the reaction time of 12 h and temperature of 70?.As for ST-B4,the optimized conditions for its synthesis of P zeolite were Na/Si=5,Si/Al=1.0,with the reaction time of 15 h and temperature of 80?.In the synthesis reaction,the phase composition of bentonite,Na/Si ratio and reaction temperature had great influence on the phase type and relative content of the synthesized products,followed by reaction time,and the effect of Si/Al ratio was the smallest.Besides,montmorillonite,clinoptilolite,cristobalite and volcanic glass could all be dissolved by alkali solution during the reaction.Activated clay prepared under the optimum conditions of atmospheric pressure had remarkable decolorization ability to unrefined edible rapeseed oil.The decolorization rate were 78.30%⁷8.57%at the absorption wavelength corresponding to chlorophyll and5.65%⁷.00% at the absorption wavelength corresponding to carotene.At the same time,other properties of activated clay also met the requirements of the national food safety standard GB25571-2011 Activated Clay for Food Additives,and could be used as food additives for refining and decolorizing edible oils.Activated clays which prepared under low-temperature calcination at atmospheric pressure by bentonite obtained from Wuhu,Anhui Province and Leping,Jiangxi Province were tested to be the first-class of national industry standards,indicating that the method has good applicability for bentonite from different areas.The calcium exchange capacity of the synthetic zeolite B1-4A,B3-4A and B4-P under the optimum conditions of one-step synthesis at atmospheric pressure were 301 mgCaCO₃/g,297mgCaCO₃/g and 313 mgCaCO₃/g,respectively,and the average particle size were 0.97?m².04?m,the whiteness were 97.0⁹8.2,and other performances also met the requirements of national light industry standard QB/T 1768-2003 Detergent 4A Zeolite,thus the synthetic zeolite could be used as detergent builders.