Study on efficient mineralization method of fly ash based on three-stage division in reaction process
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摘要:
粉煤灰由于含有钙镁等碱土金属氧化物导致其浆液呈碱性，直接充填井下采空区易污染地下水源。利用陕北矿区府谷电厂粉煤灰开展组分测试、浆液pH值特性测试及固碳降碱试验，基于浆液pH值与OH−浓度理论关系对粉煤灰固碳降碱反应过程进行阶段划分并提出两级耦合的粉煤灰高效矿化方法。研究结果表明：①粉煤灰含CaO、MgO、K2O等碱土金属氧化物，溶于水浆液呈高碱特性，浆液pH值随浆液浓度增大而增大，当粉煤灰浆液质量分数≥30%时，浆液pH值不受质量分数影响且粉煤灰碱土金属氧化物与水反应生成OH−速率较快，溶于水20 min，OH−浓度饱和；②粉煤灰与CO2发生矿化反应生成方解石型CaCO3，每1 kg粉煤灰可矿化封存29.57 g CO2；③粉煤灰与CO2发生矿化粉煤灰固碳降碱过程中pH变化曲线呈“倒S”型，按降pH速率分为慢速（I）、快速（II）、慢速（III）3个阶段，3个阶段的pH值分界点分别为11.39、7～8且第I阶段无法消除；④降pH与降碱不是同一概念，降碱指的是降浆液中OH−浓度，降pH第I阶段对应快速降碱阶段，降pH第II、III阶段对应深度降碱阶段；⑤决定粉煤灰固碳量的主要为降pH第I阶段，而非pH下降速率较大的第II阶段，第I阶段CO2利用率约为30.78%，第II、III阶段CO2总利用率约为9.04%；⑥基于粉煤灰固碳降碱过程阶段划分及反应装置降碱速率、容积的差异性，提出两级耦合的粉煤灰高效矿化方法。研究结果对分析粉煤灰固碳降碱机理，提高粉煤灰固碳降碱效率，促进粉煤灰处置工业化应用具有重要意义。
Abstract:Due to alkaline earth metal oxide such as calcium and magnesium being existed in the fly ash, its slurry is alkaline. It’s easy to pollute the underground water when the slurry was filled in the goaf. Thus, some experiments such as composition test, slurry pH characteristic test, carbon and alkali reduction test were carried out by using fly ash selected from Fugu Power Plant in northern Shaanxi Mining area. Based on the theoretical relationship between slurry pH value and OH− concentration, the reaction process of carbon and alkali reduction of fly ash was divided into stages and a two-stage coupling method for high efficiency mineralization was proposed. The results showed that the slurry of fly ash had high alkali for the reason that the alkali metal oxides such as CaO,MgO,K2O,etc being existed and the pH value increased with the slurry concentration. While the pH value was not affected by the concentration when the slurry concentration was more than 30%. At the same time, the OH− concentration was saturated after fly ash being dissolved in water for 20 minutes due to the fast reaction of alkali earth metal oxides with water. And the reaction product is calcium carbonate of calcite type as well as 20 grams of carbon dioxide being mineralized per kilogram of fly ash. In the process of carbon fixation and alkali reduction, pH reduction curve reflected as reverse S type and the pH reduction rate was divided into three stages, referring to slow, fast and slow. The changing points of three stages were that pH values being 11.39 and 7−8 as while as the first stage cannot be eliminated. Simultaneously, the pH value and alkali reduction were not the same concept for alkali reduction referring to the decrease of OH−concentration in the slurry. So the first stage corresponded to the rapid alkali reduction and the second and third stage corresponded to the deep alkali reduction. The carbon fixation amount was mainly determined by the first stage, not the second stage of rapid pH value decrease for the reason thar the CO2 utilization rate of the first stage was about 30.78%, while the total CO2 utilization rate of the second and third stages was about 9.04%. Based on the stage division of reaction as while as the difference of alkali reduction rate and reaction device volume, a two-stage coupling method of high efficiency mineralization was proposed. The research results have great significance for analyzing the mechanism of carbon fixation and alkali reduction of fly ash, improving the efficiency and promoting the industrial application of fly ash disposal.
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图 1 不同时间条件下不同浓度粉煤灰浆液pH值
Figure 1. pH values of different concentrations of fly ash slurry at different times
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图 4 反应前后粉煤灰矿物相组成
Figure 4. Mineral phase composition of fly ash before and after reaction
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图 6 矿化前后粉煤灰浆液质量分数及失重速率
Figure 6. Mass percentage and mass loss rate curve of fly ash slurry before and after reaction
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图 7 不同反应装置降pH过程及阶段划分
Figure 7. pH reduction process and stage divisions of different reaction devices
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图 8 pH值与c（OH−）关系及降碱过程阶段划分
Figure 8. Relationship between pH and OH− concentration and stage divisions according to alkali reduction process
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图 10 反应装置进出气口CO2体积分数
Figure 10. CO2 concentration at inlet and outlet of reaction unit
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图 11 相同反应条件下不同反应装置降pH过程
Figure 11. pH reduction process of different reaction devices under same reaction conditions
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图 12 两级耦合的粉煤灰高效矿化工艺流程
Figure 12. High efficiency mineralization process of fly ash with two-stage coupling
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图 13 涡流式与旋桨式联合反应降pH过程
Figure 13. pH reduction process of vortex and paddle reaction combined
表 1 粉煤灰组分XRF分析成果
Table 1 Components of fly ash by XRF spectrometric analysis
组分 SiO2 Al2O3 CaO Fe2O3 K2O MgO Na2O P2O5 SO3 TiO2 其他 质量分数/% 46.9 19.5 17.8 9.4 1.6 1.1 0.9 0.9 0.8 0.8 0.3 
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表 2 固碳降碱试验方案
Table 2 Carbon fixation and alkali reduction test scheme
方案编号 气量/（m3·h−1） 浆液质量分数/% 试验装置 1 50 17 涡流式 2 134 25 涡流式 3 75 30 涡流式 4 125 30 涡流式 5 125 30 旋桨式
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