Preparation And Performance Of Activated Carbon/Zeolite Composite Adsorptive Materials From Coal Gasification Coarse Slag

With the rapid development of coal gasification industry,a large amount of coal gasification coarse slag?CGCS?has been produced.The main chemical components of coal gasification coarse slag are SiO₂,Al₂O₃ and residual carbon.At present,the main treatment method of CGCS is landfill,and has not been effectively utilized,and there is little research on the utilization of CGCS.Zeolite and activated carbon play an important role in gas or liquid separation,purification and water treatment as single-factor adsorbents.However,the adsorbents combine the adsorptive properties of both zeolite and activated carbon are often required in actual production.In this paper,CGCS was used as the main raw material to prepare the activated carbon/zeolite composite materials,which provides a new reasonable route for the utilization of CGCS.The carbonaceous component in coarse slag was activated by steam,and the aluminum and silicon components were converted into zeolite crystals by hydrothermal crystallization.In this paper,the influence of different steam activation conditions on the activation process of carbonaceous components was studied.The effects of different hydrothermal crystallization conditions on the zeolite type and crystallinity in the composite were studied.And the structure,morphology and properties of the composites were characterized.Furthermore,the adsorption capacity of the composite for organic dyes and heavy metal ions was investigated.The effect of different steam activation conditions on the activation of carbonaceous components in coarse slag was investigated.It can be seen that keeping the activation time of steam unchanged and increasing the activation temperature can speed up the activation process.Keeping the activation temperature constant,the predominant pore structure in coarse slag changed from micropores to mesopores with increasing the activation time.When the activation temperature was 800°C and the activation time was 1h,the specific surface area of coarse slag reached the maximum,which was 77.75 m²/g.And the value of micropore area was 36.10 m²/g.Thermal gravimetric and differential thermal analyses?TG/DTA?showed that the carbonaceous component was about 11.9%in the activated coarse slag,which was lower than unactivated coarse slag.Scanning electron microscopy?SEM?showed that activated carbonaceous composition kept a loose state.After the coarse slag was activated by steam,different types of zeolite/activatedcarbon composites were obtained by controlling different hydrothermal conditions.The optimal synthetic conditions for zeolite X/activated carbon composites were found to be as follows:pretreatment of hydrochloric acid concentration,8%;directing agent,3 mL;alkalinity,6%;crystallization temperature,100°C;crystallization time,15 h.The optimal synthetic conditions for P-type zeolite/activated carbon composites were found to be as follows:pretreatment of hydrochloric acid concentration,8%;alkalinity,5%;crystallization temperature,120°C;crystallization time,8 h.P-type zeolite/activated carbon composites which had a relatively broad preparation condition were easier to synthesize.Experiment results confirmed that carbonaceous component contained in the raw was essential to the hydrothermal process which converted aluminosilicate into zeolite.SEM images showed that the special octahedral crystals of the zeolite linked with activated carbon surface in the composite;P-type zeolite crystals were spherical and its surface is rough,closing to the carbonaceous components in the composite.From thermal gravimetric and differential thermal analyses,the content of activated carbon in X-type zeolite/activated carbon composites prepared under the optimal conditions was about 26.67%.And the pore structure analysis showed that the composite had both mesopore and micropore structure,the specific surface area reached 294.98 m²/g,including the specific surface area which was 194.08 m²/g,the total pore volume was 0.3355 cm³/g and the average pore size was 4.55 nm.The prepared X-type zeolite/activated carbon composite were used to adsorb methylene blue and Cr³⁺in aqueous solution.The results showed that when the initial concentration of methylene blue solution was 50 mg/L,adsorption time was 5 h,the amount of composite was 0.5 g/L,the adsorption amount of the composite for methylene blue was 93.88 mg/g and the removal reached above 90%.When the initial concentration of Cr³⁺was 10 mmol/L,adsorption time was 5 h,the amount of composite was 10 g/L,the adsorption capacity for Cr³⁺was 0.766 mmol/g and the removal was above 85%.The performance of the composite will be very useful for its potential application in sewage treatment and other fields.