# Arsenic (V) Removal by an Adsorbent Material Derived from Acid Mine Drainage Sludge
## 1 Introduction  
Arsenic exists as oxides in the soil, sediment, and water in many parts of the world and originates from both natural and anthropogenic activities. Arsenic (V) (As(V)) is the predominant species under oxidizing conditions, specifically as oxyanions of arsenic acid (H3 AsO4, H2 AsO4-, H2 AsO4-, and AsO43-), while arsenic (III) (As(III)) exists as arsenious acid (H3 AsO3, H2 AsO3-, and HAsO32-) under mildly reduced conditions [1]. Arsenic presents a high danger to human health when present in drinking water and, as such, toxicity related to arsenic is a severe concern worldwide. Arsenic compounds are recognized as Group 1 carcinogens by the International Agency for Research on Cancer (IARC) [2]. The World Health Organization currently recommends a maximum contaminant level (MCL) of arsenic in drinking water of 10 ug/L [3]. In Korea, the standard for arsenic in drinking water has been set at 10 ug/L, with 50 ug/L as the maximum allowable concentration in rivers and lakes as regulated by ambient water quality standards [4]. Arsenic pollutants are prevalent in developing countries such as Argentina, Chile, China, Mongolia, Nepal, and other Southeast Asian countries [5]. In recent years, 94% of Asian regions have a risk of arsenic contamination in excess of 10 ug/L in drinking water from wells and, in some countries, concentrations reach more than 50 ug/L [6]. The mining sector, in particular, is the primary anthropogenic source of arsenic contamination. Acidmine drainage (AMD) is the runoff produced, when water contacts exposed rocks that contain sulfur-bearing minerals, which react with water and air to form sulfuric acid and dissolved iron [7]. This acidic runoff dissolves heavy metals such as arsenic, which pollute ground and surface water. Mining in areas with scarce water resources presents many problems. In these cases, it is necessary to evaluate drinking water for toxic contaminants and mitigation techniques to remove any heavy metals. For example, ground and surface water pollution in Mongolia has been relatively poorly studied and arsenic pollution is anticipated to increase due to mining activities [8]. During the mining season, the major rivers in northern Mongolia become polluted by heavy metals such as Mn, Al, Cd, and As [9]. Separately, in Korea, many abandoned metal mines have been improperly managed, and environmental issues continuously emerge in the areas' nearby closed mines [10]. A wide range of technologies can remove arsenic from water, such as membrane separation, ion exchange, coagulation, precipitation, and adsorption [11; 12]. Among the many techniques currently available for removing arsenic from water, adsorption is considered to be one of the most promising because of the low cost, high efficiency, and ease of operation [13; 14]. Many studies have exploited zeolite, chitosan, granular ferric hydroxide (GFH), and other materials as adsorbents to remove arsenic [15; 16]. Iron-based adsorbents have attracted much interest due to their high efficiency in arsenic remediation, environmental friendliness, and abundance on earth [11]. Extensive studies have been conducted on iron-containing adsorbents with high affinities for arsenic species. Iron-containing oxides have high surface activities due to surface hydroxylation and ionization under certain medium conditions, which vary surface charge [17]. We aimed to develop an iron-based adsorbent from waste materials. Large quantities of sludge are generated during AMD treatment processes, and this waste material consists of amorphous micron- and submicron-sized metal oxide/hydroxide particles with high specific surface areas [18; 19]. The most abundant elements in AMD sludge are Fe and Al, which are known to effectively remove arsenic [15; 20]. Thus, we anticipate that sludge would have high potential for arsenic adsorption. In this study, an iron-based adsorbent called MIRESORBTM was prepared from coal mine drainage sludge, a byproduct of coal mine drainage treatments.