Natural red clay as an efficient and reusable catalyst in the heterogeneous Fenton reaction for wastewater treatment

Abstract Olive mill wastewater (OMW) exhibits substantial contaminated properties due to its high content of organic substances, such as phenolic constituents. This research aims to study the viability of using natural and low-cost mineral clay with acceptable iron content (Fe 2 O 3 content = 10.8%) as an adsorbent and as a catalyst for the degradation of organic matter in a real industrial olive mill wastewater throughout heterogeneous Fenton-like reaction. The maximum removal efficiency achieved through adsorption was 30–33% for 40 to 40 g/L of NRC. The NRC, as a catalyst, has been used in its natural form and after thermal treatment activation at 850°C in order to eliminate undesirable organic material, carbonates and interstitial water. In both cases, the catalyst has been characterized using XRD, scanning electron microscope, and FT-IR analyses. The degradation efficiency of organic matter by natural red clay (NRC) and incinerated clay (INRC) was up to 64.2% and 70.8%, respectively. The total phenolic compounds removal at the end of the reaction using NRC and INRC as catalysts without pH modification of the reaction medium were 73.5% and 87.6%, respectively. Moreover, the studied natural materials NRC and INRC retained their performance after 4 and 6 cycles, respectively, demonstrating their potential to be used as low-cost catalysts. This potential was verified by XRD and FT-IR characterization. Overall, the results obtained showed that NRC and INRC could be used as suitable, efficient and low-cost catalysts for the treatment of OMW at an industrial level by means of Fenton-type reactions.