Production of ceramic pellets with micrometric zero-valent iron as an active phase for chemical reduction of contaminants in water

OCAMPO, SANTIAGO; MOCCIARO, A.; HERNANDEZ M; RENDTORFF, N. M; GARCÍA EINSCHLAG, F. S.; CARLOS, L.

Congreso; WCCE11, XI Congreso internacional de Ingeniería Química; 2023

The use of micro and nanometric zero-valent iron (mZVI) for water treatment has received special attention in recent decades due to its low cost and high effectiveness. The processes that use mZVI allow the removal of a wide variety of contaminants through various mechanisms that include: direct chemical reduction, adsorption on corrosion products, surface precipitation, and/or co-precipitation [1, 2]. Until now, the use of mZVI is limited due to difficulties in its method of obtaining and because, depending on the different application scenarios, problems may arise in the hydraulic transport of the particles, problems associated with its stability in suspension and passivation of its surface due to the inherent corrosion of the application medium. However, it is possible to overcome some of these limitations by designing support materials for the mZVI that give it new features [2]. This work shows the results of the designing and making of ceramic pellets with micrometric iron as an active phase for water treatment. Micrometric iron was prepared by traditional ball milling of steel wool as precursor material. Cylindrical pellets with a diameter of 4mm and a length of 6mm were made by extrusion of a mixture of water, commercial clay, and carbon black as a pore forming agent. Different milling conditions were tested (steel wool dry milling; steel wool with green tea infusion wet milling; steel wool with 10% carbon black dry milling), different iron/clay mass ratios (50/50; 40/50; 30/70), and different calcination conditions and temperatures (500 °C, 600 °C, 700 °C and 800 °C in air and 500 °C under vacuum). The obtained materials were characterized by measuring the amount of resulting active iron, the open porosity by the Archimedes immersion method in water, and the resistance to immersion in water. The crystalline phases of the pellets were determined by X-Ray Powder Diffraction (XRD) in order to evaluate the thermal transformation of the clay and iron phases. To assess the removal capacity, chemical reduction tests were carried out using orange G as a model contaminant in batch-type systems at pH 5 under N2 or air. The resulting pellets showed porosities ranging from 35% to 45%, without a notable effect of the calcination temperature on the porosity and good water immersion resistance. The materials calcined in air showed amounts of iron lower than 3%, while the materials calcined at 500 °C in vacuum showed values around 25% of iron on a mass basis. The chemical reduction tests of orange G showed the great potential of these materials as water treatment agents and lay the foundations to continue studying improvements in the elaboration and design of these materials.