Granulated Fe-Mn bimetal-oxides: A reusable adsorbent for mercury removal and valorisation of spent adsorbent as a retarding agent and compressive strength enhancer in cementitious materials

• Published in: Process safety and environmental protection 2024-04, Vol.184, p.1293-1305
• Main Authors: Naga Jyothi, M.S.V., Vajitha, G., Gandhi, T. Pushparaj, Ramaiah, B.J., Maliyekkal, Shihabudheen M.
• Format: Article
• Language: English
• Subjects: Compressive strength enhancer; Disposal; Mercury immobilisation; Retarding agent; Ultrasonic pulse velocity; Waste valorisation
• ISSN: 0957-5820
• DOI: 10.1016/j.psep.2024.02.031

Fe and Mn-based nanoscale materials are excellent substrates for preconcentrating and recovering heavy metals in water. However, the practical use of nanomaterials is limited because of the complexity of solid-liquid separation and the potential escape of nanoparticles into the environment. Besides, there is a need to develop safe and affordable processes to valorise spent nanomaterials. The paper demonstrates an application of a granulated FeOOH-MnxOy oxides nanocomposite for heavy metal removal in water, taking mercury as a model pollutant. The work also demonstrates the valorisation of the spent adsorbent as a retarding and compressive strength-enhancing agent in cement-based materials. The granular adsorbent showed mercury adsorption capacity of 108.54 mg/g. The adsorption behaviour was evaluated thoroughly in the influence of various environmental parameters and discussed. A possible mechanism of interaction of cement and spent FeOOH-MnxOy granules is also proposed. An optimum dose of 1.5% of spent absorbent with respect to cement enhanced the compressive strength of cement mortar by 19%. Ultrasonic pulse velocity measurement is used to evaluate spent adsorbent-loaded cement retardation behaviour. The toxicity characteristic leaching procedure (TCLP) test data confirmed that mercury leaching is negligible and validates the safe disposal of spent adsorbent. [Display omitted] •FeOOH-MnxOy is a practical adsorbent with Hg(II) adsorption capacity of 108.54 mg/g.•An in-depth discussion on mechanisms of mercury adsorption onto Fe-Mn oxides.•Recycling of spent adsorbent as an active admixture in cementitious materials.•FeOOH-MnxOy acts as a retarder and enhances the compressive strength of mortar.•A safe and viable strategy to immobilise spent adsorbent in cement matrix..