Adsorptive and catalytic properties of nepheline mud

Abstract

Aluminium production is accompanied by formation of ecologically dangerous gases (HF, SO2, CO, etc). There is offered the method of purification of waste gases from ecologically dangerous components. This method is concluded in their adsorption on nepheline mud, which is alumina production waste from nepheline ore. Nepheline mud is formed during the leaching from sintered material of sodium alluminate, whereupon it has a highly developed surface, similar to the zeolite surface. Dicalcium silicate (Ca2SiO4) is the basis (85%) of nepheline mud. Nepheline mud contains 3.5% of iron oxides, which, together with highly-developed surface, gives it the catalytic properties. Dicalcium silicate can react with flourhydric acid and sulphur acids with formation of fluorite and calcium sulphate. Adsorptive and catalytic abilities of nepheline mud were investigated by anode gas drawing from Söderberg electrolyzers threw the mud layer in the socket (70 mm diameter) with the rate of 8 l/min. The socket contained 300 g of dry nepheline mud. 21 testings were carried out (2 hours each). The total volume of the gas, drawn threw the socket, was 20 260 l. The composition of HF, SO2 and СО in gases at the input and output of the socket was analyzed. The following averaged results were obtained according to the carried out testings. The content of HF in gases was reduced from 428 at the input of the socket to 4.9 mg/m3 at the output of the socket (98.85% of HF were adsorbed by mud). Content of SO2 was reduced from 730 to 36.3 mg/m3 (95% was adsorbed). As a result of the catalytic properties of nepheline mud, and the process of oxidation of carbon monoxide, its content in gases was reduced from 5960 to 46.5 mg/m3 (approximately by 100 times). The offered method may be used by aluminium plants for anode gas purification and for deep gas purification from harmful impurities before their atmospheric emission.