Ozone Assisted Leaching of Metallic Tin


Ozone Assisted Leaching of Metallic Tin

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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.

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