Journal ofNadezhda Chemical Kazakova,Technology Biserka and Metallurgy, Lucheva, 55,Petar 1, 2020,Iliev 223-227 A STUDY ON THE CEMENTATION PROCESS OF NON-FERROUS METALS FROM A BRINE LEACHING SOLUTION Nadezhda Kazakova, Biserka Lucheva, Petar Iliev Department of Metallurgical Technologies, Electrotechnics and Electronics Received 10 June 2019 University of Chemical Technology and Metallurgy Accepted 30 September 2019 8 Kliment Ohridski, Sofia 1756, Bulgaria E-mail: [email protected] ABSTRACT The initial solution obtained from brine leaching of zinc ferrite cake is used to study the cementation process of lead, silver and copper. The optimum parameters of the brine leaching stage are: NaCl concentration of 250 g/l, o H2SO4 concentration of 5 g/l, a temperature of 60 C, and a pulp density of 12.5 %. Two series of experiments are carried out using different cementation agents - iron and zinc powders. The effects of the cementation agent con- sumption, the temperature, the time and the solution initial pH on the cementation metals degree are investigated. The results obtained show that the cementation with a zinc powder leads to higher cementation degree of silver, lead and copper indicating that the repeated use of the pregnant solution aiming to leach new portions from the zinc ferrite cake is most probably favored. Keywords: cementation, zinc ferrite cake, silver, lead, copper. INTRODUCTION zinc to be more effective than iron and aluminum [3]. In fact, zinc has a lower oxidation potential than that The treatment of a zinc ferrite cake with H2SO4- of iron and therefore is a better precipitant. Although NaCl solution results in a high degree of extraction of aluminum has a lower oxidation potential than zinc, the silver and other metals. The mass of the cake under the protective oxidation layer formed on its surface during conditions applied is reduced by 50 %. The copper ex- the cementation leads to worse results. In this work, as traction from a zinc ferrite cake depends strongly on the the real leaching solution contains a significant amount temperature, the acidity of the medium and the duration of zinc, the use of a metal other than zinc would lead to of the extraction. The high degree of copper extraction is a greater contamination of the solution and would surely associated with a high iron extraction rate. The obtained hamper the zinc recovery at a later stage [4]. solutions contain up to 10 g/l Fe [1]. The results obtained in ref. [4] provide the conclu- The cementation can be described as an electro- sion that cementation with zinc may be used to remove chemical precipitation of a metal by another more copper from solutions containing zinc and iron. The use electro-negative metal. This process has been used for of zinc is chemically and environmentally favorable, centuries in hydrometallurgy for purification of the because zinc is the main component of the real leach- leaching solutions, and also for recovering the toxic and ing solution. precious metals from the industrial waste streams [2]. The temperature affects the rate of cementation in a The use of several metals for copper cementation different way. When the temperature increases, copper is already studied by a number of authors, who report cementation is accelerated, but the cementation of cad- 223 Journal of Chemical Technology and Metallurgy, 55, 1, 2020 mium deteriorates. At high temperatures, the cadmium EXPERIMENTAL dissolves in a slightly acidic solution due to the low The cementation process was carried out with pro- hydrogen overvoltage and the oxidation of the metal by duction solution obtained after leaching of zinc ferrite the oxygen contained in the solution [5]. cakes in presence of NaCl. The parameters used were Other researchers [6] describe the cementation of as follows: lead from chloride solutions using aluminum powder. • 1 h duration; The results show that pH increase from 4 to 6 decreases • a temperature 60оС; the cementation efficiency. The increase of the solution • H2SO4concentration of 5 g/l; initial pH prior to the cementation results in the precipi- • NaCl concentration of 250 g/l. tation of lead as a hydroxide. The experiments were conducted by making a com- At an initial pH value of the solution below 4, the parison between cementation with a zinc powdered agent cementation process is delayed due to the release of and an iron powder. The following parameters of the hydrogen according to the reaction: cementation process were investigated: the effect of the + 2+ Pb + 2H = Pb + H2 cementing agent consumption, the effect of the process The increase of the lead concentration in the solution temperature, the effect of pH and the process duration decreases the degree of cementation. on Ag, Cu and Pb cementation degree. The influence of the different parameters on the The experiments aimed to determine the effect of degree of cementation of lead from chloride solutions is the cementing agent consumption were performed with studied in ref. [7]. It is found that the degree of lead ce- 50 ml of the production solution at 60°C for 1 h. The mentation increases with an increase of the temperature zinc powder consumption varied from the stoichiometric at a given sponge iron consumption. The influence of the value required for cementation of Cu, Ag and Pb to a iron consumption on the degree of lead cementation at 200 % excess. different process duration and a temperature of 60° C is investigated. The experimental results showed that the RESULTS AND DISCUSSION stirring of the solution with the cementing agent has a favorable effect on the cementation of lead. The higher Effect of the cementing agent consumption on the the excess iron, the higher the degree of lead cementation degree of cementation of copper, silver and lead is. The present investigation is focused on the effect of The results obtained are presented in Fig. 1. It is evi- zinc and iron powders on the metals cementation of the dent that with 200 % excess of the zinc powder the degree production solution obtained from H2SO4-NaCl leaching of cementation of copper, silver and lead is the highest, zinc ferrite cake. almost 100 %. In case of the stoichiometrically required Fig. 1. Effect of the zinc powder consumption on the metal cementation degree. 224 Nadezhda Kazakova, Biserka Lucheva, Petar Iliev Fig. 2. Effect of the iron powder consumption on the Fig. 3. Effect of the iron powder consumption on the metal cementation degree at 40oC. metal cementation degree at 60oC. Fig. 4. Effect of the temperature on the metal cemen- Fig. 5. Effect of the temperature on the metal cemen- tation degree (Zn powder). tation degree (Fe powder). amount (100 %) of the zinc powder, the degree of cementa- does not affect the degree of cementation of silver and tion of copper and silver is about 10 % lower than that in copper with an iron powder. presence of 200 % excess of the zinc powder, whereas the degree of cementation of lead in presence of the stoichio- Temperature effect metrically required amount (100 %) of the zinc powder is The degrees of cementation of silver, copper and 55 %. This suggests that better cementation of lead can be lead at 200 % zinc consumption and temperature values carried out with a 200 % excess of a zinc powder. of 20°C, 40°C and 60°C are presented in Fig. 4. The The results referring to the cementation of metals graph shows that the degree of cementation of lead at from brine leacing solution with participation of an iron 40°C is 96 %, while that at 20°C and 60°C is 98 %, most powder at 40°C and 60°C (Fig. 2 and Fig. 3) show that likely due to an error within the limits of the chemical the degree of cementation of copper and silver increases analysis. The results of the conducted experiments show highly with an increase of the iron powder consumption that the temperature does not affect the degree of ce- above the stoichiometric one. Under these experimental mentation of silver, copper and lead with a zinc powder. conditions the degree of cementation of lead is unsatis- The results of the cementation experiments with an factory. The results of the conducted experiments show iron powder show that in the same temperature range the that the temperature value increase from 40°C to 60°C temperature does not affect the degree of cementation 225 Journal of Chemical Technology and Metallurgy, 55, 1, 2020 Fig. 6. Effect of the initial pH on the metal cementa- Fig. 7. Effect of the initial pH on the metal cementa- tion degree (Zn powder). tion degree (Fe powder). of silver and copper. The degree of cementation of the may be due to the re-dissolution of the cement sludge. metals concerned at an iron consumption increased to On the other hand, the pH increase of the brine solu- 200 % above the stoichiometric one at 40°C and 60°C tion results in precipitation of the trivalent iron contained is presented in Fig. 5. The achieved degree of cementa- in the solution. This will contaminate the cement sludge tion of silver at 60°C amounts to 96.85 %, while that of and degrade its quality. copper is equal to 95.16 %. It is worth adding that the degree of cementation of these metals is even higher in Process duration effect the case of zinc cementation. Fig. 8 shows the effect of the process duration on the Fig. 5 shows that the degree of cementation of lead cementation degree of Cu, Ag and Pb at 20°C. The zinc under these conditions increases slightly with a tempera- powder consumption is 200 % above the stoichiometric ture increase to 60°C reaching 11 %.