Phosphate removal by low-cost industrial byproduct iron shavings: Efficacy and longevity

Authors: AI, HAIPING - Case Western Reserve University (CWRU); ZHANG, KAI - Case Western Reserve University (CWRU); Penn, Chad; ZHANG, HUICHUN - Case Western Reserve University (CWRU)

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2023
Publication Date: 10/16/2023
Citation: Ai, H., Zhang, K., Penn, C.J., Zhang, H. 2023. Phosphate removal by low-cost industrial byproduct iron shavings: Efficacy and longevity. Water Research. https://doi.org/10.1016/j.watres.2023.120745.
DOI: https://doi.org/10.1016/j.watres.2023.120745

Interpretive Summary: The degradation of surface waters is often attributed to excess dissolved phosphorus (P) losses from soils. Such losses of P trigger algal blooms which cause economic and ecological impairment. Few conservation practices are able to prevent losses of dissolved P from high P soils. However, P removal structures can serve as a filter to trap dissolved P from flowing water before it reaches a surface water body; such filters require use of an effective and economical filter media. One of the most promising materials is metal shavings. This research investigated the ability of by-product metal shavings to sorb P from solution under various chemical conditions, and then develop a regeneration technique to re-use the media again. The most effective regeneration method utilized sodium hydroxide and simultaneous heating of the sample. Re-use of the material for P removal was then repeated and then followed by several successful regeneration cycles. The recommendations produced in this study will result in an appreciable cost- and resource-savings through regeneration of the metal shavings media in P removal structures that improve water quality.

Technical Abstract: Iron shaving (IS) is a low-cost industrial byproduct that shows great potential in the removal of low concentration of phosphorus (P) from contaminated water. This work aims to investigate the effectiveness of IS for P removal. Initially, IS was treated with 2.5% NaCl solution for 1-5 days to accelerate the surface oxidation, with 4-d treatment the best. The P adsorption capacity during batch experiments increased from approximately 1.0 to 2.5 mg/g after the 4-d treatment. In the column test, the P removal efficiency remained at 60+% over 60 days with the capacity at 4.1 mg/g. To regenerate the spent IS, we treated it with 1N NaOH for P desorption and then neutralized the remaining NaOH with HCl solution (pH=2). Following the first round of regeneration, the P adsorption capacity slightly decreased from 2.14 to 1.94 mg/g. To evaluate the longevity of IS, we conducted 7 adsorption-regeneration cycle tests and the P adsorption capacity only slightly decreased to around 1.75 mg/g. By comparing an intermittent 10-s induction heating and an isothermal hot NaOH (85 ') treatment in 10-min desorption tests, (95.3% versus 56.6% regeneration), we found that induction heating was an efficient IS regeneration method. In addition, SEM/EDX, XRD, and XPS tests were conducted to track the changes in the morphology, crystallinity, and surface oxidation products of IS in the cycle tests. Generally, when IS was recycled for multiple rounds, its surface changed from coarse to smooth with fewer reactive sites and an increased presence of Fe3O4, which should be the main reason for the decreasing P adsorption capacity over time. Overall, this study establishes the foundation for the real-world application of IS to P removal from agricultural runoff.