What's causing this high SO2 concentrations in Kazakhstan?
The source of SO2 is the smelter associated with the Jezkazgan (Zhezkazgan, Жезказган) copper mine, mined by Kaz Minerals. The complex also produces sulfuric acid.

If you check for the other atmospheric pollutants with ventusky.com, you will see associated particulate matter - PM 2.5 and PM 10.