Aluminum mobility in mildly acidic mine drainage: Interactions between hydrobasaluminite, silica and trace metals from the nano to the meso-scale

Abstract

Aluminum precipitates control the hydrochemistry and mineralogy of a broad variety of environments on Earth (e.g., acid mine drainage, AMD, coastal wetlands, boreal and alpine streams, tropical acid sulfate soils, laterites and bauxites, …). However, the geochemical and mineralogical processes controlling Al (and other associated metals and metalloids) transport and removal in those environments are not fully understood. The geochemical system of Paradise Portal (Colorado, USA) comprises sulfate-rich mildly acidic waters, the hydrochemistry of which is directly controlled by the massive precipitation of hydrobasaluminite Al 4 (SO 4 )(OH) 10 •12-36H 2 O. Three connected but discernible aluminum precipitation stages were identified and described: 1) nanoparticle formation and size decrease along the creek, 2) hydrobasaluminite neoformation on the riverbed, and 3) precipitate accretion and accumulation on the riverbed leading to Al and Fe banded formations. The co-occurrence of Al and Si in the system was observed, recording significant amounts of Si accompanying the three different components of the system (i.e., nanoparticles and fresh and aged Al-precipitates). Also, abrupt and minor changes in the sedimentary record were described and proposed to be the response of the system to seasonal and interannual changes in AMD chemistry. Concerning the mobility of other metals and metalloids, P, Th, V, W, Ti and B showed a tendency to be preferentially incorporated into hydrobasaluminite, while others like Be, As, Se or Ba tend to remain dissolved in the water.

Geochemical Modeling of Iron and Aluminum Precipitation during Mixing and Neutralization of Acid Mine Drainage

“…It is safe to say that the difference between 0.28 mg/L and 0.006 mg/L can be attributed to colloidal iron particles getting through the filter [33]. Similar nanometer size ranges have been documented for hydrobasaluminite [34].…”

“…Indeed, silica is required to precipitate from mass balance considerations [33] during the oxidation of pyrite and often reaches silica solubility limits. Caraballo et al [34] have identified a silica coating on hydrobasaluminite precipitating from the Paradise Portal in Colorado. The form of the silica is not usually known.…”

Geochemical behavior of rare earth elements in acid drainages: Modeling achievements and limitations

“…Silica was present in all basaluminite analyses, with Al/Si molar ratios between 21 and 180, with the highest ratio in DB, 500 m from the water mixing. A similar distribution of Al/Si ratios was reported by Caraballo et al (2019).…”

Settling of Iron and Aluminum Particles in Acid Solutions for Acid Drainage Remediation

“…Schwertmannite, Fe(OH) 3 (a), hydrobasaluminite, and Al(OH) 3 were the iron and aluminum phases chosen to precipitate in the simulations. These meta-stable phases were selected, as they are the most probable minerals to rapidly form in systems affected by acid mine drainage, at the pH range studied (pH 4.5-6.5) [7,34,45,46]. Hydrobasaluminite was preferred to basaluminite because the latter is formed by the dehydration of hydrobasaluminite [34], a process that is not expected in our suspensions.…”