How to remove Ca and Na in high purity alumina
Removal of Ca impurities
Ca impurities can be removed by extraction agent, chemical precipitation, salting-out crystallization, ion exchange, chelating agent and other methods.
Extraction solvent extraction can use first difficult solubility of calcium sulphate, make Ca ₂ + in the form of CaSO4 precipitate out, coupled with other methods (such as solvent extraction, etc.) for a second removal. Extraction agent P ₂ m1, also known as phosphate 2 hospital vinegar, D2EHPA, cheap, is a kind of acid extraction solvent, extraction of metal ions is order from big to small in the order: Fe3 +, Zn2 +, Cu2 +, CO2 +, M92 +, Mn2 +, Ca2 +. Hong-yan xie adopts P ₂ m1: extracting a mixture of calcium magnesium, manganese, calcium ions markedly reduced, but can't reach the requirement of high purity. Zhao Hong Tao et al. carried out a deep removal of Ca impurities in phosphogypsum. Through the study, both soluble impurities and insoluble impurities in phosphogypsum can be effectively extracted by the organic solvent tributyl phosphate, and finally calcium sulfate particles with a purity of more than 99% were obtained.
Calcium ions are precipitated by oxalate in the form of precipitation. The removal rate of calcium ions is ideal.
The calcium and magnesium ions in lithium bicarbonate system were removed effectively with the high selectivity of ion exchange resin.
In crude oil, Ca was mainly removed by chelating and removing Ca. Wang Qing et al. carried out comparative studies on the removal effect of several decalcium agents and analyzed the reasons, among which HEDP was superior to EDTA in removing Ca and was the best decalcium agent. HEDP, also known as hydroxy ethyldiphosphate, can form a six-ring chelate with Ca2+, which has a good scale inhibition effect. It is better when used in combination with polycarboxylic acid scale inhibition dispersant, usually with a concentration of 1 ~ 10 mg/L.
Removal of Na impurities
The commonly used methods to remove sodium impurities in preparation of alumina include washing method, water heat treatment method and boric acid addition method. Lu Wen used elution method to remove sodium from aluminum ammonium sulfate crystals. He believed that when aluminum ammonium sulfate crystals were heated to 150-200℃, bubbles would appear in the crystals, which was conducive to elution of sodium impurities. In the preparation of aluminum oxide, Li Jiahong compared the water heat treatment method and the boric acid method, because the purity of aluminum oxide obtained by hydrothermal method is higher than that by boric acid method, finally the hydrothermal method is chosen. In the process of calcining aluminum hydroxide, boric acid is added to make it react with sodium impurities to form sodium metaborate, and then the aluminum oxide is pickled and dried, and finally the aluminum oxide with sodium content less than 0.001% is obtained.
In addition, high purity potassium hydroxide (KOH) is widely used in a variety of industrial fields (e.g., the manufacture of potassium compounds, pharmaceuticals and synthetic resins, semiconductor processing, electronics, etc.), especially in the electronics field, where it has a high economic value. It is prepared from industrial-grade potassium chloride and its properties are greatly affected by impurities containing sodium ions. In general, sodium ions are removed by recrystallization. Yoon H et al. proposed an electrochemical system of sodium manganese oxide and potassium hexafluorite, which can selectively remove about 36% sodium ions in raw material potassium chloride, which is very beneficial to the industrial production of high-purity potassium hydroxide. Moreover, this electrochemical cell system is applicable not only to seawater desalination, but also to resource recovery.
This provides a new idea for impurity ion removal. The selective ion separation system can be applied to the removal process of other impurity ions. If the sodium ion impurity is selectively removed, the sodium ion battery material that is known to be selectively inserted and deembedded with sodium ions can be used.
