Evaluate electrochemical methods of extraction of rare metals in Kazakhstan.
Electrolysis is one of the main methods of obtaining rare metals, alloys and refining the crude metal.
Electrolysis is the decomposition of the electrolyte by a constant electric current, which is accompanied by the formation of new substances. On the electrodes occur the oxidation reaction – recovery: the anions at the anode give up electrons and are oxidized and the cations are recovered at the cathode.
In the electrolytic refining of the metal anode dissolves rough. In this case the polarization is caused by increase of concentration of metal ions in the anode space. The limit of increasing concentration is to saturation and subsequent precipitation of salt on the anode surface, which leads to a sharp increase in resistance and drop the current density (salt passivation of the anode). Impurities included in the crude anode, can form a separate phase. The potential of the anode is determined by the most electronegative component of the mixture more positive components is not dissolved.
Niobium and tantalum
NbCl5, TaCl5, NbF5 and TaF5 to form complex compounds of the type K2MeF7. Fornybar potassium easily hydrolyses to K2NbO5F5*H2O. Fortuntely more sustainable. When recovering the formed halides of lower valency.
Components of the electrolyte to obtain both metals are KCl, K2MeF7, KF, in some cases, the use of oxides dissolved in the fluoride melt. The values of the decomposition potential of the following:
The electrolysis process is carried out with a high cathodic current density of 1-2 a/cm2, which allows to achieve a capacity of discharge of ions M3+ and ME2+ and to prevent their accumulation and disproportionation.
The niobium and tantalum used open cells. The cathode material is molybdenum. The composition of the electrolyte: 9-10% K2MeF7, 4-8% Me2O5, 25-42% KCl, 44-57% KF.
Introduction in the electrolyte of dissolved oxides improves the wettability of the anode and increases the critical current causing an anode effect. Improved wetting due to the fact that oxides are surface-active substances. Supplement of soluble oxides in the melt reduces the contact angle.
The electrolysis temperature of 750 C, the current efficiency of 80%. The purity of The technical, mass. %: 0.1 To 0.2 On, 0.1 To 0.3 Fe+Ni, 0,01 F, Mn 0,002, 0,003-0,1 C.
For obtaining metals of high purity are used without electrolytes Me2O5 in a sealed cell. The electrolyte composition: 55 percent KCl, 27.5% of KF, 17.5% of K2MeF7. The temperature is 700-800C, cathode current density of 0.6-0.8 a/cm2, anode 1.5 to 2.3 a/cm2. The resulting niobium contains, mass. %: 0.02; <O 0,05$ 0,02 N.
Used in the technology and the process of electrolytic refining of anode made from metal powder by sintered metal. In this case, the chloride electrolyte is used consisting of KCl, NaCl, MeCl3. In fluoride melts, the ions Nb5+, Ta5+ bound in solid complex, and highlight the need to apply higher voltage. That entails joint discharge more electronegative ions. Conducting electrolysis in a closed electrolytic cells improves the purity of the metal. Wherein the electrolyte is removed from the cathode Deposit by vacuum separation at 1800-2000C.