Fenton like oxidation of Orange II with natural argentinian diatomites

N INCHAURRONDO; JOSEP FONT; P HAURE

Bacelona

Congreso; 13th Mediterranean Congress of Chemical Engineering (13MCCE); 2014

Diatomite is an abundant, low cost material, widely available from a sustainable source. Its composition includes mainly opal or hydrous silica (SiO2-H2O) but also alumina, iron, alkali metal oxides, and a minor amount of other impurities, such as P2O5 and TiO2. This natural material is commonly used as adsorbent and catalyst support, yet the presence of a relatively high percentage of iron would enable its use as heterogeneous Fenton-like catalyst without requiring major modifications. In this contribution, thermally treated Argentinean diatomite (0.4 wt% Fe) was used as Fenton-like catalyst for the degradation of the azo-compound Orange II (OII) in a laboratory batch reactor. The raw diatomite was sieved between 7 and 8 mesh (2.38-2.83 mm). Then, calcination was carried out at three different final temperatures, 500, 700 and 1000 °C, under air atmosphere in a programmable furnace. Fresh and calcined samples were thoroughly characterized. Calcination resulted in the removal of impurities, the skeletal structure of diatoms partially collapse at higher temperatures, but the original geometry was mostly preserved. Upon calcinations, the Fe percentage increased from 0.41 % (raw) to 0.45 % (700 °C) and the shrink and hardening of individual particles was generated. This may have contributed to the gradual reduction of the surface area from 79 m2/g (raw) to 35 m2/g (700°C). Preliminary experiments discarded the effect of adsorption on OII removal in the pH range 3 to 4. Orange II Fenton-like tests were performed varying the diatomite calcination temperature, reaction temperature (50, 60, 70, 80°C); catalyst load (0.48, 0.96, 1.92 and 3.84 g), H2O2 dose (10.96, 13.7, 20.55 mmol/L) and pH (2-4). Complete decoloration (100%) and TOC abatement (68 %) were achieved after 240 min at 70°C using a catalyst concentration of 0.96 g/L and the stoichiometric requirement of oxidant. The amount of Fe leached was less than 1 mg/L. The diatomite catalyst performance is comparable or even better to that reported in literature, using an OII concentration higher than the commonly evaluated.