Naturally-occurring iron minerals as inexpensive catalysts for CWPO

Abstract

This work explores the potential application of naturally-occurring minerals as inexpensive catalysts in heterogeneous Fenton, namely catalytic wet peroxide oxidation (CWPO). The availability, low cost and environmentally friendly character of those materials make them interesting candidates for such application. The performance of magnetite, hematite and ilmenite as CWPO catalysts has been tested under different working conditions, which include temperature (25–90 °C), H2O2 dose (250–1000 mg L−1) and catalyst concentration (1–4 g L−1). The operating temperature plays a key role on the rate of H2O2 decomposition so that with magnetite H2O2 conversion after 4 h increased from 8 to 99% by increasing the temperature from 25 to 90 °C. Based on the reaction mechanism proposed, a kinetic model was developed which successfully described the experimental results on H2O2 decomposition. The catalytic performance of the minerals tested at temperatures above the ambient was demonstrated using phenol (100 mg L−1) as target pollutant. Unprecedented efficiencies of H2O2 consumption, higher than 80% were achieved, allowing high oxidation and mineralization, i.e. complete phenol conversion and almost 80% TOC reduction at 75 °C with a catalyst loading of 2 g L−1 and the theoretical stoichiometric amount of H2O2 for complete mineralization of phenol (500 mg L−1). Magnetite is particularly attractive, since it showed the highest activity and can be easily separated from the liquid phase given its magnetic properties. All the minerals tested suffered low iron leaching and magnetite and hematite showed a good reusability upon three consecutive runs. However, in this case long-term durability is not a crucial issue, given the availability and low cost of these mineralsThis research has been supported by the Spanish MINECO through the project CTQ2013-4196-R and by the CM through the project S2013/MAE-2716. M. Muñoz thanks the Spanish MINECO for a Juan de la Cierva-Incorporación postdoctoral contract (IJCI-2014-19427

Preparation of Al/Fe-Pillared Clays: Effect of the Starting Mineral

“…However, as far as we know, such a type of impurities have not shown direct influence on the catalytic behavior of the materials (for instance, by transition metals located at structural sites of the phases catalyzing the reaction). In spite of very recent studies claiming the CWPO catalytic activity displayed by naturally occurring minerals [ 47 ], they have been mostly iron-rich minerals (namely, hematite, magnetite and ilmenite) exhibiting in addition significant Fe-leaching, pretty longer times and higher temperatures of reaction than those reported here.…”

Metal organic frameworks as precursors for the manufacture of advanced catalytic materials

“…(e) Iron (Fe)-MOFMS Iron minerals are ubiquitous in nature and there is abundant availability of them at minimal cost. 109 Haematite is the most common iron containing ore, but iron is widely distributed in other minerals such as magnetite and taconite. The melting point of metallic Fe is 1538 1C, its boiling point is 2861 1C and the reduction potential of Fe 3+ and Fe 2+ are À0.04 and À0.41 V, respectively.…”

Condensation By-Products in Wet Peroxide Oxidation: Fouling or Catalytic Promotion? Part I. Evidences of an Autocatalytic Process

“…Metal leaching is an irreversible process associated with the presence of organic acids in the reaction medium, refractory species commonly formed upon the oxidation of organic pollutants, which promote the complex formation and mobilization of iron [5]. Fe supported on Al 2 O 3 or robust iron minerals appear as the most resistant catalysts to iron leaching [4,8,9] but, unfortunately, it cannot be completely avoided, especially with highly-polluted wastewaters, where organic acids will be formed in significant amounts. In this context, the use of metal-free catalysts has gained great importance in recent years.…”