Complex Aluminum Electrolyte Composition Analysis And Molecular Ratio Correction

Liquid temperature of aluminum electrolyte depended on its molecular ratio and currency efficiency was also directly affected, so molecular ratio was an important parameter that should be analyzed and controlled on time in the process of aluminum production. Acidic electrolyte was widely used in the modern aluminum electrolytic industry. Cryolite, alumina and excessive aluminum fluoride were the main components of aluminum electrolyte. Besides, a modicum of additives such as CaF2, MgF2, LiF and KF which were used to improve the performance of aluminum electrolyte were contained generally. Due to existence of numerous components, the composition of aluminum electrolyte became quite complicated, which made the previous formula and determination of molecular ratio need to be corrected and improved in order to meet the actual needs of modern aluminum production. In this paper, determination of various components in aluminum electrolyte and effects of additives such as KF, CaF2, MgF2 and LiF to molecular ratio were studied. Furthermore, molecular ratio formula of fluoride ion selective electrode method was revised. The main contents were as follows:(1) The level of alumina in aluminum electrolyte sample was determined respectively by xylenol orange spectrophotometric method, weight method and improved weight-spectrophotometry. Through comparing these methods, following conclusions were drawn:Xylenol orange spectrophotometric method was characteristic of time saving, simple apparatus, but the results of determination were relative high. Weight method was time consuming and tedious in the process of constant-weighing, simultaneously, the reproducibility of method was poor. The improved weight-spectrophotometry for the assay of alumina in aluminum electrolyte was more accurate and had better precision, though its operation was a bit more complex than other methods.(2) Estimation of various additives in complex aluminum electrolyte was studied with Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Analytical conditions such as digestion procedure of samples, operating parameters of instrument, selection of analytical wavelength and observation direction were explored and optimized. A method for determination of KF, CaF2, MgF2 and LiF in the aluminum electrolyte was established with ICP-OES after wet digestion. As relatively high accuracy was found through measurement of standard samples, this method could be used for determining of additives in the aluminum electrolyte samples.(3) Currently, neither national nor industrial standard analytical method of elements in aluminum electrolyte has been officially released. A method for simultaneously determining K, Ca, Mg, Li, Al and Na in aluminum electrolyte by ICP-OES with wet digestion was studied. The present methodology gave recoveries in the range of 94.57^102.97%. The relative standard deviation was as follows:K<3.40%, Ca<3.38%, Mg<2.91%, Li<2.41%, Al<9.70%, Na<9.64%. Certain reference for building standard analytical method and preparing standard sample of aluminum electrolyte was offered by this study.(4) After wet extraction, the content of potassium in raw materials provided Qinghai Branch of Aluminum Corporation of China, for example, alumina, aluminum fluoride, cryolite and so on, were analyzed by ICP-OES. It was seen that different contents of potassium were found in raw materials. In order to reduce the introduction of potassium into aluminum electrolyte, selective use of raw materials was needed, or these raw materials were used in aluminum production after potassium was removed.(5) Take determination of molecular ratio in fluoride ion selective electrode method for instance, correction for the formula of molecular ratio was studied. The content of sodium fluoride or aluminum fluoride in aluminum electrolyte was determined by fluoride ion selective electrode method. Variety of experimental conditions were explored and optimized in the experimental process. Phases of various components in aluminum electrolyte were researched with X-ray diffraction and effects of additives to molecular ratio formula were investigated. The formula presently used for calculation of molecular ratio was corrected, accordingly molecular ratio formula suitable for complex aluminum electrolyte containing four kinds of additives, for instance, KF, CaF2, MgF2 and LiF, were obtained.