Purification of process solutions from mercury by sorption

Abstract

At JSC «Uralelectromed», selenium-containing raw materials and industrial products are processed, resulting in solutions containing a mixture of mercury with concentrations as follows (g/dm3): 157–210 Se; 0.004–0.02 Hg; 0.15–0.20 Te; 2–3 As; 0.15–0.20 Sb; and 45–50 S. To produce branded selenium, the mercury concentration in the solution must be kept below 0.001 g/dm3. Various methods, such ashydrometallurgical and electrochemical processes, are known for mercury purification from solutions. JSC «Uralelectromed» has selected sorption technology for mercury removal using the weak-base macroporous anionite Lewatit MP-68 (Germany), which allows for control over the degree of solution purification. In pursuit of import substitution for the Western European sorbent Lewatit MP-68, we investigated several pre-selected industrial sorbents for extracting mercury anionic complexes produced in Russia (AM-2B, AN-31, AV 17-8, VP-3Ap), China (Seplite MA 940 and LSC 710), and India (Tulsion CH-95 and CH-97). Initially, in static mode, we determined the distribution coefficient (Cd), the degree of element extraction (ε), the static exchange capacity of the resins (SEC, g/dm3), and the mercury/selenium separation coefficient (DHg/Se) which led to the selection of the best samples: AV 17-8, Seplite MA 940, AM-2B, and CH-97, with SEC values of 0.95–0.97 g/dm3 (SEC = 0.98 g/dm3 of resin Lewatit MP-68). Subsequently, in dynamic mode, we ranked the ionites by decreasing dynamic exchange capacity (DEC / TDEC): AV 17-8 ≥ Lewatit MP-68 > AM-2B > Seplite MA 940 > Tulsion CH-97. Resins AV 17-8, Seplite MA 940, and AM-2B demonstrated similar dynamic sorption characteristics; under comparable conditions, mercury breakthrough occurred after processing at least 950 specific volumes of the initial solution. In contrast, with Lewatit MP-68 ionite, mercury breakthrough occurred after no more than 750 specific volumes, indicating the need to increase the number of sorption steps in the solution purification cascade. Considering the totality of ion-exchange properties, for further industrial testing, it is recommended to use the domestically produced resin AV 17-8 instead of the foreign sorbent Lewatit MP-68 in the sorption purification process of selenic acid to remove mercury, thereby ensuring the production of branded selenium.