添加AlF_3铝熔体除碱热力学分析及其在HX系统中应用

Thermodynamic analysis of alkaline removal of aluminium melt by adding AlF_3 and its application in HX system

针对电解铝液除Na、Ca等碱金属问题,选择用AlF_3粉末加氩气作为除碱剂,并开发了HX除碱工艺和设备。热力学分析表明,AlF_3与铝熔体中Na、Ca的反应在较大温度范围内可满足反应自由能ΔG<0的条件,且反应产物不会影响铝熔体成分;HX系统采用旋转喷吹技术可以使AlF_3粉末和氩气与铝熔体均匀混合,不仅显著提高了除碱率,而且避免了以往使用氯气造成的环境污染和设备腐蚀等问题;通过工艺研究,获得除碱工艺的最佳处理时间为15 min,最佳处理温度为800℃;生产实践表明,处理后Na质量分数可降至1.8×10-6,除Na率为90.9%;平均Ca质量分数可降至0.2×10-6,除Ca率为94%,是一种环保高效的除碱技术。

In order to solve the problem of removing alkali metals such as Na and Ca with electrolytic aluminum solution, AlF 3 powder and argon were selected as alkali-removing agents and HX process and equipment were developed for alkali-removing. Thermodynamic analysis results show that Gibbs free energy Δ G 〈0 was satisfied for the reaction of AlF 3 with Na and Ca over a wide temperature range, and the chemical composition of aluminum melt wouldn’t be changed. The spin rotor technology was used, which dispersed AlF 3 powder and Argon in aluminum melt uniformly. It not only increases the rate of alkali removal significantly, but also avoids environmental pollution and equipment corrosion caused by the use of chlorine gas in the past. Process studies obtained the optimal time and temperature of alkaline removal treatment, which were 15min and 800℃ respectively. Application results showed that the sodium level was decreased to 1.8×10 -6 and the removal rate was 90.9% on average, and the calcium level was decreased to 0.2×10 -6 and the removal rate was 94% on average, which means the new technology is efficient and environment-friendly.