Abstract
Hydrogen peroxide with its high oxidising potential is commonly used in hydrometallurgical extraction of metals from ores, anode slimes and waste materials (e.g. WEEE) and treatment of cyanidation effluents. Main detraction to H2O2 is its rapid catalytic decomposition leading to prohibitively high consumption. Effect of pH (0-4), Cu(II) (0-10 g.l-1) and temperature (20-80°C) on H2O2 stability was investigated using response surface methodology. Influence of neutral-alkaline conditions (pH 7.3-11.8) and presence of solids (1-20% w/v) was also tested. A polycarboxylate based solution (PBS) was utilised to improve H2O2 stabilisation. The significance order of parameters on H2O2 decomposition was temperature > pH > Cu(II). Elevating the level of these parameters increased H2O2 decomposition. The activation energy (60.7±2.5 kJ.mol-1) indicated a chemically controlled process. Alkaline conditions (up to pH 11.8) led to higher H2O2 decomposition. Presence of solids adversely affected H2O2 stability under certain conditions. The addition of PBS significantly improved (up to 54%) H2O2 stability in the presence of copper. The presence of PBS in H2SO4-H2O2 leaching of waste of printed circuit boards (WPCBs) enhanced copper extraction by up to 19%. PBS can be suitably utilised to stabilise and hence reduce H2O2 consumption in aqueous solutions particularly in the presence of copper.
Highlights
Hydrogen peroxide (H2O2) has been employed in many industrial applications due to its superior features including high oxidation potential (+1.78 V) [1], easy handling-storage and environmentally friendly nature i.e. formation of no toxic by-products during the oxidation process (Eq 1) [2,3]
A polycarboxylate based solution (PBS with a trade name of Polycar-100 produced by Iksa [35] (Table 1) was utilised as the additive to improve the stability of hydrogen peroxide
The results have demonstrated that decomposition of hydrogen peroxide aggravates with increasing temperature, pH and copper in descending order of significance
Summary
Hydrogen peroxide (H2O2) has been employed in many industrial applications due to its superior features including high oxidation potential (+1.78 V) [1], easy handling-storage and environmentally friendly nature i.e. formation of no toxic by-products during the oxidation process (Eq 1) [2,3]. Hydrogen peroxide is effectively used in chemical oxidation of cyanidation effluents containing free and weak acid dissociable (WAD) cyanides [14,15,16,17]. Application field of hydrogen peroxide includes waste treatment such as direct oxidation of inorganic (e.g. sulphide (S2-), nitrite) and organic contaminants (e.g. formaldehyde, thiols) in drinking/natural water, oxidation of organics using advanced oxidation processes (AOP) (Fenton’s process (Fe2+/H2O2) or H2O2/UV/O3) [3,18,19]. Hydrogen peroxide is prone to catalytic decomposition resulting in increased reagent consumption, which may lead to an adverse effect on process economics [16]. 10-11), despite the theoretical consumption of hydrogen peroxide for the oxidation of free cyanide is 1.31 g H2O2 per g CN-, in practice, this increases by 1.5-6.1 fold [16]. Yazıcı and Deveci [27]
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