Kinetic Study on the Preparation of Aluminum Fluoride Based on Fluosilicic Acid

Gaoxiang Chen,Xingdong Yang,Jianhong Luo,Zhiye Zhang,Lan Sun,Jiyan Qu

doi:10.2478/pjct-2021-0024

Abstract

Abstract Reasonable mathematical derivation and mechanism model in the process of producing aluminum fluoride by fluosilicic acid is the key to the industrial treatment of fluorine resources in the tail gas of phosphate ore. In this work, aluminum fluoride was generated directly by fluosilicic acid to extract fluorine from the tail gas of phosphate rock. The uncreated-core model dominated by interfacial reaction and the uncreated-core model dominated by internal diffusion-reaction were then respectively utilized to describe the reaction kinetics of the generation of aluminum fluoride. The result showed that the uncreated-core model was dominated by interface reaction and internal diffusion, the apparent reaction order n = 1, and the activation energy Ea = 30.8632 kJ · mol–1. Product characterization and kinetic analysis were employed to deduce the reaction mechanism of preparing aluminum fluoride. The theoretical basis for the low-cost recycling of fluorine resources in the tail gas of industrial phosphate ore was provided in this work.

Highlights

The recovery and reuse of fluorine in the tail gas of phosphate ore are one of the key technologies to realize environmentally friendly phosphorus chemical industry[1, 2]
Aluminum hydroxide was considered to have insufficient internal voids for external fluids to diffuse into aluminum hydroxide, the uncreated-core model was superior to the homogeneous model
The kinetic mechanism of the reaction between aluminum hydroxide and fluosilicic acid was analyzed by measuring the yield of silica at different temperatures, and the following conclusions were drawn: (1) The kinetic results showed that the uncreated-core model was suitable for the reaction of fluosilicic acid with aluminum hydroxide, which was controlled by internal diffusion and interfacial reaction

Summary

Introduction

The recovery and reuse of fluorine in the tail gas of phosphate ore are one of the key technologies to realize environmentally friendly phosphorus chemical industry[1, 2]. The production methods of aluminum fluoride mainly included three kinds of fluorite as the main raw material: wet method, dry method, non-water method and fluosilicic acid as the main raw material: ammonia method, direct method, monohydrate method[5, 6, 7]. Among the three methods using fluosilicic acid as the main raw material, the direct reaction method has gained the favor of industry for the low cost and simple operation process[6]. As the main raw material of wetprocess phosphoric acid in China’s phosphorus chemical industry, phosphate ores containing 3–5% fluorine have attracted extensive attention in the fluorine chemical industry. The effective recovery of fluorine from the tail gas of wet process phosphoric acid was a problem concerned by industry. There were phase transition and contamination problems in the direct method using fluosilicic acid as a fluorine source, the purity and bulk density of aluminum fluoride was a major challenge[11, 12]

Methods

Results

Conclusion