rhodium catalysts are used as they are highly efficient and can be infinitely recycled and are hence the lowest cost option however iron in the form of its fe iii and fe ii oxides would probably be more effective than lead in achieving the required catalysis to regenerate nohso 4 it is well known that despite the high efficiency of esp systems wet fgd systems receive tons per day of fly ash containing a broad cocktail of iron and numerous other heavy metals thus in a real plant situation metals catalysts are abundant within the wet fgd liquor and possibly also on the oxidised surfaces of the baffles of the demisting unit it can be envisaged that the conditions to generate h 2 so 4 exist within the scrubber liquor it is also probable that this h 2 so 4 is largely captured in the gypsum carbonate caso 4 caco 3 wet fgd liquor however different conditions arise in the demisting zone above the spray system of the wet fgd here we have u2018 plant water u2019 sprays and no alkali to absorb the h 2 so 4 thus favourable conditions arise to generate h 2 so 4 but not remediate it in such conditions h 2 so 4 can be generated and released up the stack carried in aerosol from the demisters the invention will become better understood when reference is made to the accompanying drawings wherein fig1 is a schematic illustration of a typical coal fired power plant configuration incorporating scr and wet fgd systems fig2 is a schematic illustration of a wet fgd scrubber system for removing.