SOLAR LIGHT ASSISTED PHOTOCHEMICAL OXIDATION OF HCHS IN AQUEOUS PHASES

COTILLAS, SALVADOR; CONTE, L.O.; LORENZO, DAVID; CARMEN DOMINGUEZ; AURORA SANTOS

Zaragoza

Congreso; XXXIX Reunión Bienal de la Real Sociedad Española de Química; 2023

Real Sociedad Española de Química

During the 20th century, lindane (γ-hexachlorocyclohexane, HCH, C6H6Cl6) was a pesticide produced and marketed worldwide. The synthesis of this compound was carried out with benzene and chlorine under UV irradiation [1]. In 2008, the European Union forbade lindane production because it was classified as a cancerogenic compound by the International Agency for Research on Cancer [2]. Despite this, uncontrolled industrial landfills still exist where chemical companies dumped tonnes of lindane and other isomers of HCH over the years, causing soil and groundwater pollution by leaching [3, 4]. In Spain, two landfills in the Aragón region (northeast of Spain) are highly contaminated by lindane production wastes (Bailín and Sardas). For this reason, it is necessary to develop clean and efficient technologies that allow the removal of HCH isomers (HCHs) from water bodies. In this context, Advanced Oxidation Processes (AOPs) can be considered an excellent alternative for removing HCHs from groundwater. These processes are based on producing large amounts of free radicals that significantly contribute to eliminating organic pollutants. Hydroxyl radical is the most common species generated in these processes due to their high oxidation potential (2.8 V). However, it is demonstrated that the ability of these radicals to degrade aliphatics can be limited, and the total mineralization of HCHs could be incomplete. With this background, this work proposes the use of solar light irradiation for the degradation of HCHs from groundwater in the presence of persulfate (oxidant) and ferrioxalate (catalyst). To do this, effluents from Sardas and Bailín landfills polluted with different HCHs were treated using a solar simulator and different dosages of oxidant and catalyst. During the process, free sulfate radicals are expected to be generated from the activation of persulfate by iron. These radicals can contribute to the degradation and mineralization of HCHs contained in groundwater. The use of ferrioxalate as a catalyst allows working under circumneutral pH conditions. Results show that it is possible to attain a total HCHs conversion up to 75 % in 600 min with the solar simulator (qw:1.12·10-7 E cm-2s-1) using 250 mg dm-3 Na2S2O8 and 3.5 mg dm-3 Fe.