Hydrogeochemistry of Alkaline Steel Slag Leachates in the UK

Abstract

Drainage from steel slag disposal sites can be extremely alkaline and a source of pollution to surface and ground waters. Data is presented detailing the hydrogeochemistry of seven highly alkaline (pH> 10) steel slag surface discharges in the UK. While there is the consistent presence of Ca-OH type groundwater in all the discharges, there are clear disparities in hydrochemical facies within and between sites, reflecting native hydrochemistry, source material and hydrogeological setting. The longevity of the pollution problem from steel slag disposal sites is highlighted at one site where the water quality records date back three decades. The consistent presence of Al, B, Ba, Fe, Sr, V and occasional presence of Cr, Mo, Ni, Pb were found at concentrations typically below surface water quality standards in the leachates. Some of the monitored metals (Al, Fe, Ni, V) were found to be lost from solution downstream of emergence in calcitedominated precipitates which rapidly form at all sites at rates up to 100 g m −2 day −1 . The low concentrations of potentially problematic trace elements in both solution and the sediments are discussed with regard development of economically viable passive treatment wetlands for highly alkaline industrial discharges.

Biogeochemical Reduction Processes in a Hyper-Alkaline Leachate Affected Soil Profile

“…Some are entirely natural, e.g., soda lakes, hot springs, oceanographic cold seeps, deep mine waters (Takai et al 2001;Takai et al 2005;Pollock et al 2007;McMillan et al 2009;Brazelton et al 2010), but many are also due to human activities. These anthropogenic sites occur as a result of the presence of residues from a range of industrial processes, e.g., lime production waste, steelworks slags, coal combustion residues, Solvay process waste, chromite ore processing residues, bauxite processing wastes, borax wastes and cementitious construction wastes (Effler et al 1991;Carlson and Adriano 1993;Townsend et al 1999;Deakin et al 2001;Ye et al 2004;Mayes et al 2006;Mayes et al 2008;Hartland et al 2009;Mayes et al 2011). Weathering of these wastes typically produces highly alkaline leachate (pH 10-13) due to the ubiquitous presence of Ca, Na and K oxides (primarily CaO) that hydrolyze in natural waters to produce soluble metal hydroxides.…”

“…In addition, due to the leaching of sulphur bearing minerals, elevated sulphate concentrations are often reported to affect overall water quality (Schwab et al 2006;Mayes et al 2008;Whittleston et al 2010). When Ca concentrations are not limiting, the alkaline leachate reacts rapidly with atmospheric CO 2 where it emerges into sub-aerial environments, sometimes producing very high rates of calcite precipitation (Deakin et al 2001;Hartland et al 2009).…”

Effect of Basic Oxygen Furnace Slag used as Structural Filling Materials on the Subsurface Environment

“…기존 연구에서는 알칼리 용출수가 수계 내 화학적 산소 요구량(Chemical Oxygen Demand, COD), Mayes et al, 2006Mayes et al, , 2008 (Peek and Volk, 1985). 전반적으로 전로제강슬래그의 영향을 받은 토양 내 오염우려물질 함량은 대체적으로 유의한 큰 변화는 없었 (Lekakh et al, 2008).…”

Main and Trace Element Distribution in Slag-Leachate-Tufa System Precipitate

“…Due to reaction of the slag material with slightly acidic to neutral rain or runoff waters, lime is hydrolysed to produce hydroxyl ions, which increase the leachate pH: CaO (lime) + H 2 O (l) → Ca 2+ (aq) + 2(OH -Alkaline waters are commonly observed to emerge from slag dumps [e.g., [7][8][9] and also from construction and transportation structures (e.g., road beds, fill material), where the slag material was used [10]. In addition to extremely high pH values, the waters are characterized by high content of total dissolved solids (TDS), oxygen depletion, tufa precipitation, the occurrence of color and odor nuisances, and the release of sulfur.…”

“…Slag-related mineral precipitation may hold rainwater, disrupt natural groundwater flow patterns, and cause bed-sediment armoring in adjacent surface-water systems [11][12]. Variations in metal concentrations of more than one order of magnitude were found in leachates from different sites [7][8]. The elements most likely to be of environmental concern in ferrous slag include As, Cr, Mn, and -rarely -Co [13].…”