Researchers in the Republic of Moldova turned walnut shells into activated carbons that remove dissolved iron from water. The study, published in Results in Engineering, used citric acid as a modifying agent and two heat treatments. One carbon was heated to 450 C in air, the other to 600 C under nitrogen. The resulting materials had very low surface area, around 0.35 to 0.98 square meters per gram, yet still captured iron effectively. That points to oxygen-rich surface groups doing the heavy lifting rather than porosity. Iron removal depended heavily on pH. At pH 2 the carbons removed only about 5 to 6 mg per gram. At pH 9 to 10 apparent removal reached 23 to 31 mg per gram, but the authors note that at alkaline pH iron can precipitate as hydroxide, so the high numbers are not purely adsorption. Langmuir isotherms fit the equilibrium data well, and pseudo-second-order kinetics described the uptake. The work is a useful example of turning agricultural waste into a water treatment material with a food-grade chemical. The authors are clear that real-world performance, regeneration, and competitive adsorption still need testing. For walnut growing regions with iron problems, it is a promising starting point, not a finished solution.
