Method for producing cryolites by using aluminum electrolytic cell cathode carbon block alkaline leaching solution

Abstract

The invention relates to a method for preparing cryolites by using an aluminum electrolytic cell cathode carbon block alkaline leaching solution, and belongs to preparation methods of the cryolites. The method comprises the following steps: grinding aluminum electrolytic cell cathode carbon blocks finely to a certain particle size, performing slurry mixing with alkali liquor, and performing agitation leaching at a heating temperature of 20-90 DEG C; then performing filtration to obtain a first filtrate and a first filter residue; adding sodium fluoride and a small amount of Na3AlF6 solids into the first filtrate; then controlling the speed of introducing NH3-rich gas or adding NH4F to generate a deposit under the action of heating agitation; and after reaction, performing filtration to obtain a second filtrate and a second filter residue, and drying the second filter residue at 100-150 DEG C to obtain a cryolite product. According to the method provided by the invention, by replacing acid leaching with alkali leaching, the requirement of a production process on equipment is reduced, treatment processes including floatation are reduced, an absorption process of hydrogen fluoride is reduced, and the treatment process is simplified; a high-temperature treatment process is not used, so that the energy consumption is reduced; and by adding a crystal seed, high-quality cryolites with uniform particle sizes are generated under the condition that the airflow rate is controlled. The method provided by the invention is simple in process, achieves closed cycle, is high in resource utilization rate and avoids secondary pollution.

Description

technical field [0001] The invention belongs to a method for preparing cryolite, in particular to a method for producing cryolite by using the alkaline leaching solution of cathode carbon block of an aluminum electrolytic cell as a raw material. [0002] technical background [0003] During the production process of aluminum electrolysis, the cathode carbon block expands due to the penetration of impurities such as sodium and cryolite, which further causes damage to the electrolytic cell. Domestic aluminum electrolytic cells need to be overhauled when they are about 2000 days old. The waste cathode carbon blocks produced during the overhaul process are one of the main solid pollutants in the aluminum electrolysis industry. The statistical results of the fluorine balance survey of industrial aluminum electrolytic cells show that for every ton of electrolytic aluminum produced, about 10kg of waste cathode carbon blocks will be produced. Taking 2015 as an example, the output of...