Predictive hydrogeochemical modelling of bauxite residue sand in field conditions

Abstract

>Geochemical and hydrological model for bauxite residue sand. >Combined hydrogeochemical simulation of bauxite residue sand under field conditions, in 2D, heterogeneous domomain. >Evaluation of management practise for the amelioration of bauxite residue sand as substrate for plant growth.This manuscript illustrates an innovative application of detailed hydrogeochemical modelling to the field of bauxite residue management. A recently developed simulation tool that combines geochemical reaction calculations in PHREEQC with variably saturated flow and transport processes in COMSOL was employed to investigate the evolution of water availability and water quality in fertigated and amended bauxite residue sand as response to rainfall leaching. The level of detail in flow and reactions calculations is novel to studies of residue management and rehabilitation. Due to the general applicability, the employed simulation and parameterization techniques are of interest to a broad audience in the field of mining waste management. Predictive Hydrogeochemical Modelling of Bauxite Residue Sand in Field ConditionsLaurin Wissmeier *,a) , David A. Barry a) and Ian R. Phillips b) The suitability of residue sand (the coarse fraction remaining from Bayer's process of bauxite 2 refining) for constructing the surface cover of closed bauxite residue storage areas was 3 investigated. Specifically, its properties as a medium for plant growth are of interest to ensure 4 residue sand can support a sustainable ecosystem following site closure. The geochemical 5 evolution of the residue sand under field conditions, its plant nutrient status and soil moisture 6 retention were studied by integrated modelling of geochemical and hydrological processes. 7For the parameterization of mineral reactions, amounts and reaction kinetics of the mineral 8 phases natron, calcite, tricalcium aluminate, sodalite, muscovite and analcime were derived 9 from measured acid neutralization curves. The effective exchange capacity for ion adsorption 10 was measured using three independent exchange methods. The geochemical model, which 11 accounts for mineral reactions, cation exchange and activity corrected solution speciation, 12 was formulated in the geochemical modelling framework PHREEQC, and partially validated 13 in a saturated flow column experiment. For the integration of variably saturated flow with 14 multi-component solute transport in heterogeneous 2D domains, a coupling of PHREEQC 15 with the multi-purpose finite-element solver COMSOL was established. The integrated 16 hydrogeochemical model was applied to predict water availability and quality in a vertical 17 flow lysimeter and a cover design for a storage facility using measured time series of rainfall 18 and evaporation from southwest Western Australia. In both scenarios the sand was fertigated 19 and gypsum-amended. Results show poor long-term retention of fertilizer ions and buffering 20 of the pH around 10 for more than 5 years of leaching. It was concluded that fertigation, 21 gypsum amendment and...

Natural evolution of alkaline characteristics in bauxite residue

“…9) only exhibit a narrow section. This neutralizing behavior is associated with the dissolution of sodalite, tricalcium aluminate, calcite and other alkaline compounds (Snars and Gilkes, 2009;Wissmeier et al, 2011). This tendency may demonstrate that fresh bauxite residue contains a larger concentration of sodalite, tricalcium aluminate and calcite, compared to aged residues (consistent with Fig.…”

“…Much of this neutralizing behavior is associated with hydroxyls on the surfaces of iron oxides (FeO,its reaction (Eq. (11) occurs at the region of pH<6) in the bauxite residue and dissolution of sodalite, 12), ( 13) and ( 14) (Snars and Gilkes, 2009;Wissmeier et al, 2011;. The length of the neutralizing region reflects the contents of these components in the bauxite residue.…”

Modelling Hydrological Performance of a Bauxite Residue Profile for Deposition Management of a Storage Facility

“…The water potential exceeded −1000 kPa (pF: 4) during long-term drought conditions (lack of intense rainfall events) (Figure 4). In this context, Wissmeier et al [51] reported that the water potential of residue sand obtained from bauxite residue did not drop below −1500 kPa (pF: 4.17) during drought conditions (periods with lack of sufficient rainfall). In our study, the high clay and silt content of the bauxite residue (i.e., fine texture of bauxite residue) affected its hydraulic parameters (i.e., high residual water content and low hydraulic conductivity) (Tables 1 and 2), and thus led to the low infiltration of water to deeper depths of the profiles.…”

VS2DRTI: Simulating Heat and Reactive Solute Transport in Variably Saturated Porous Media

“…The module fully implements all of the capabilities of the general‐purpose geochemical reaction model PHREEQC (Parkhurst and Appelo ), including temperature‐dependent interactions between water and minerals, gases, ion exchangers, surface complexers, and solid solutions. The capability for users to define reactants and kinetic rate expressions allows PHREEQC to be used for simulating a wide range of biogeochemical processes, such as geologic sequestration of carbon dioxide (Garcia‐Rios et al ), transport of arsenic in the environment (Campbell and Nordstrom ), acid mine drainage (Shim et al ), fate of residues from mining and mineral processing (Wissmeier et al ), and impacts of agricultural practices on groundwater quality (Ledesma‐Ruiz et al ).…”