# Arsenic (V) Removal by an Adsorbent Material Derived from Acid Mine Drainage Sludge
## 4 Conclusions  
Arsenic pollutants are prevalent in developing countries. Thus, locally available and low-cost adsorbent materials are promising technological solutions for arsenic removal for water treatment at the local level. This study evaluated the physical characteristics and arsenic adsorption performances of new MIRESORBTM adsorbent materials that were derived from iron-rich acid mine drainage sludge. The materials were also compared with commercially available adsorbent GFH. The specific surface area, pore volume, and pore size of powdered MIRESORBTM were 233.48 m\({}^{2}\)/g, 0.57 cm/g\({}^{3}\), and 7.30 nm, respectively. While the surface area of the MIRESORBTM absorbent was lower than GFH, the relatively larger pore openings supported more efficient mass transport of aqueous arsenic, in agreement with adsorption kinetic experiments. The half-life time of MIRESORBTM was 2.5 h, which was 2.68 times faster than that of GFH. The maximum adsorption capacity of MIRESORBTM was 50.38 mg/g, and N2-sorption isotherms were fit more accurately to the Freundlich model than Langmuir adsorption. Superior arsenic adsorption performance was achieved in MIRESORBTM materials under lower pH conditions due to electrostatic interactions between the adsorbent and adsorbate.  
The feasibility of MIRESORBTM materials to be used for practical applications in water treatment was evaluated by experiments using environmental samples of AMD, using lab-scale column and pilot-plant formats. Using a short EBCT of 11.8 min, the lab-scale column could be operated up to 5840 BV without a breakthrough. Judicious tuning of operating conditions achieved more than 90% arsenic removal efficiency for MIRESORBTM materials during pilot-plant operation. Thus, MIRESORBTM materials derived from iron-rich acid  
Figure 7: Results from pilot-scale experiments of arsenic removal by using MIRESORBTM as an adsorbent material.  
mine drainage sludge is a highly efficient and economical material for removing arsenic from wastewater.  
The following are available online at [[https://www.mdpi.com/2076-3417/11/1/47/s1](https://www.mdpi.com/2076-3417/11/1/47/s1)]([https://www.mdpi.com/2076-3417/11/1/47/s1](https://www.mdpi.com/2076-3417/11/1/47/s1)), Figure S1: Experimental set-up for lab-scale column test, Figure S2: Scanning electron microscope images of (a) MIRESORB\({}^{\text{TM}}\) and (b) GFH, Figure S3: Arsenic removal efficiency from As(V) in DI water and an environmental sample of AMD. The initial As(V) concentration was 50 mg/L, the adsorbent dose was 1 g/L, the contact time was 48 h, and the initial pH was 6.0, Figure S4: SEM/EDS images of (a) fresh and (b) spent GFH, Figure S5: SEM/EDS images of (a) fresh and (b) spent MIRESORB\({}^{\text{TM}}\).  
Conceptualization, S.D.K., W.H.J., and Y.H.; investigation, E.B. and J.S.; resources, W.H.J. and S.D.K.; writing--original draft preparation, E.B. and J.S.; writing--review and editing, T.-H.K. and Y.H. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2020R1A6A1A0304274211). [PERSON] acknowledges the financial support from Seoul National University of Science and Technology.  
We acknowledge the Mine Reclamation Corp. of Korea for providing overall resources for investigation, including the raw sludge for adsorbents, the test site for pilot-study, and the idea for recycling sludge.  
The authors declare no conflict of interest.