Ozone Assisted Leaching of Metallic Tin

Andrea Miskufova, Patrik Kuruc, Anna Kochmanova, Tomas Havlik, Hedviga Horvathova

Tin belongs to critical metals for EU mainly for energy technologies (SET-plan) and it occurs practically in all electronic devices. In an effort to save and recover this element from electric and electronic waste (WEEE) the possibility for intensification of tin leaching by use of oxidative agent – ozone was studied in this work. As the WEEE represents an extremely heterogeneous system composed of various kinds of metals and materials, experimental work was first dealing with study of pure tin metal behaviour during ozone assisted leaching. The ozone produced in ozone generator was bubbling continuously during defined time through leaching solution placed in glass reactor. The production of ozone by ozone generator (expressed in grams of O3 per hour) as well as its solubility in sulphuric acid solutions was measured by iodometric analysis. At the beginning, the influence of sulphuric acid concentration (1 – 3 M) and temperature of solutions (20, 30, 50 °C) on ozone solubility was tested. After that, the extraction of tin (~ 5 x 3 x 1 mm cut pieces of pure metal) during leaching in sulphuric acid continuously saturated with ozone at constant flow was investigated. The influence of acid concentration, time and temperature as well as ozone flow rate on tin extraction was monitored. The extraction values for tin during leaching by use of ozone were always compared with those obtained without ozone action. Results showed that temperature of solution has detrimental effect on ozone solubility. On the contrary, acid concentration in the range of 1 – 3 M H2SO4 has positive effect on ozone solubility. Tin was not extracted after leaching for 2 hours in 1 M H2SO4 without ozone and after 6 hours of leaching in the same media the extraction represented only 2 %. However, after bubbling of ozone through the solution at ozone flow rate 7 g/hr at standard conditions (101 kPa, 20 °C), the extraction after 2 hours was enhanced to 15 % and after 5 hours increased to around 70 %. It was shown, that by presence of ozone during leaching in H2SO4 at standard conditions, it is possible to intensify the leaching process and tin extraction efficiency significantly. The main limiting factor of tin extraction was ozone flow during leaching. The influence of acid concentration on tin extraction was less essential. The solubility of tin species present in the solution and tin saturation during leaching played some role in the leaching process efficiency, too.