ABSTRACT

The content and depolymerization degree of the glass phase in coal fly ash (CFA) is positively correlated with the activity of CFA, which is one of the key factors in the comprehensive utilization of this ash. At present, the most common and accurate method for quantitative analysis of fly ash is selective dissolution. However, more experimental data are needed to specify the effect of HF concentration on reaction kinetics, the dissolution rate of amorphous phases, and the formation of new amorphous and crystalline phases. In this study, the effects of reaction temperature, reaction time, and hydrofluoric acid concentration on the leaching rate of CFA were investigated with a single-factor condition experiment and orthogonal experiment. Phase composition and transformation of CFA under different conditions were observed with XRD and SEM. The results show that with increasing reaction time (5–120 min), temperature (20–80°C), and HF concentration (5% to 30%), the leaching rate of CFA also increased from 29.4% to 90.2%. The phase transformation of CFA in acid solution is as follows: in 5% hydrofluoric acid concentration solution, the original glass phase disappears totally and a new glass phase is formed; in 15% hydrofluoric acid concentration solution, quartz disappears and a new phase named ralstonite [Na_0.5Mg_0.5Al_1.5F₄(OH)₂ · (H₂O)] is formed; and when the hydrofluoric acid concentration reaches 30%, mullite disappears and a new phase named potassium aluminum fluoride (KAlF₄) is formed. Also, when the temperature rises to 80°C, the f-CaO in CFA participates in the reaction to form creedite (Ca₃Al₂SO₄F_7.5(OH)_2.5 · 2H₂O) and fluorite (CaF₂). Reaction kinetics demonstrate that the leaching reaction to the glass body of CFA is a diffusion-controlled process, and the apparent activation energy of the Si and Al leaching reaction in glass phase is 11.62 kJ/mol and 26.039 kJ/mol, respectively.

摘要

粉煤灰（CFA）中玻璃相的含量和解聚度与CFA的活性呈正相关，是粉煤灰综合利用的关键因素之一。目前，粉煤灰定量分析最常用和最准确的方法是选择性溶解。然而，需要更多的实验数据来确定 HF 浓度对反应动力学、非晶相溶解速率以及新的非晶相和晶相形成的影响。本研究采用单因素条件试验和正交试验研究了反应温度、反应时间和氢氟酸浓度对CFA浸出率的影响。用XRD和SEM观察了不同条件下CFA的相组成和相变情况。结果表明，随着反应时间（5~120 min）、温度（20~80°C）和HF浓度（5%~30%）的增加，CFA的浸出率也从29.4%提高到90.2%。CFA在酸溶液中的相变如下：在5%氢氟酸浓度溶液中，原来的玻璃相完全消失，形成新的玻璃相；在 15% 的氢氟酸浓度溶液中，石英消失，形成新相，称为 ralstonite [Na_形成0.5 Mg _0.5 Al _1.5 F ₄ (OH) ₂ · (H ₂ O)]；当氢氟酸浓度达到30%时，莫来石消失，形成新的氟化铝钾（KAlF ₄）相。另外，当温度升高到80℃时，CFA中的f-CaO参与反应，生成creedite（Ca ₃ Al ₂ SO ₄ F _7.5 (OH) _2.5  · 2H ₂ O）和萤石（CaF ₂）。反应动力学表明，CFA对玻璃体的浸出反应是一个扩散控制的过程，Si和Al在玻璃相中的浸出反应的表观活化能分别为11.62 kJ/mol和26.039 kJ/mol。