Geochemical Speciation Model Research Articles

Dissolved Organic Carbon Reduces Uranium Bioavailability and Toxicity. 2. Uranium[VI] Speciation and Toxicity to Three Tropical Freshwater Organisms

The influence of dissolved organic carbon (DOC) on the toxicity of uranium (U) to three Australian tropical freshwater species, the Northern Trout Gudgeon (Mogurnda mogurnda), green hydra (Hydra viridissima) and unicellular green alga (Chlorella sp.) was assessed. Exposures were conducted in synthetic soft water without DOC and with DOC added in the form of standard Suwannee River Fulvic Acid (SRFA). Organisms were exposed to a range of U concentrations at a range of DOC concentrations (0-20 mg L(-1)). U toxicity was up to 20 times less in water containing 20 mg L(-1) DOC, relative to DOC-free test waters. U toxicity was also assessed using natural water from a tropical Australian billabong containing 10 mg L(-1) DOC. U toxicity was up to ten times less in the billabong water, relative to DOC--free test waters. SRFA was twice as effective at reducing U toxicity as the billabong water at equivalent DOC concentrations. Geochemical speciation modeling confirmed the decreased U toxicity that resulted from both DOC sources was primarily due to a decrease in the free uranyl ion (UO2(2+)) through complexation with DOC. A predictive model is presented for each of the organisms that can be used to predict U toxicity at a given U and DOC concentration.

Dissolved Organic Carbon Reduces Uranium Bioavailability and Toxicity. 1. Characterization of an Aquatic Fulvic Acid and Its Complexation with Uranium[VI

Fulvic acid (FA) from a tropical Australian billabong (lagoon) was isolated with XAD-8 resin and characterized using size exclusion chromatography, solid state cross-polarization magic angle spinning, 13C nuclear magnetic resonance spectroscopy, elemental analysis, and potentiometric acid-base titration. Physicochemical characteristics of the billabong FA were comparable with those of the Suwannee River Fulvic Acid (SRFA) standard. The greater negative charge density of the billabong FA suggested it contained protons that were more weakly bound than those of SRFA, with the potential for billabong water to complex less metal contaminants, such as uranium (U). This may subsequently influence the toxicity of metal contaminants to resident freshwater organisms. The complexation of U with dissolved organic carbon (DOC) (10 mg L(-1)) in billabong water was calculated using the HARPHRQ geochemical speciation model and also measured using flow field-flow fractionation combined with inductively coupled plasma mass-spectroscopy. Agreement between both methods was very good (within 4% as U-DOC). The results suggest that in billabong water at pH 6.0, containing an average DOC of 10 mg L(-1) and a U concentration of 90 μg L(-1), around 10% of U is complexed with DOC.

An evaluation of biotic ligand models predicting acute copper toxicity to Daphnia magna in wastewater effluent

The toxicity of Cu to Daphnia magna was investigated in a series of 48-h immobilization assays in effluents from four wastewater treatment works. The assay results were compared with median effective concentration (EC50) forecasts produced by the HydroQual biotic ligand model (BLM), the refined D. magna BLM, and a modified BLM that was constructed by integrating the refined D. magna biotic ligand characterization with the Windermere humic aqueous model (WHAM) VI geochemical speciation model, which also accommodated additional effluent characteristics as model inputs. The results demonstrated that all the BLMs were capable of predicting toxicity by within a factor of two, and that the modified BLM produced the most accurate toxicity forecasts. The refined D. magna BLM offered the most robust assessment of toxicity in that it was not reliant on the inclusion of effluent characteristics or optimization of the dissolved organic carbon active fraction to produce forecasts that were accurate by within a factor of two. The results also suggested that the biotic ligand stability constant for Na may be a poor approximation of the mechanisms governing the influence of Na where concentrations exceed the range within which the biotic ligand stability constant value had been determined. These findings support the use of BLMs for the establishment of site-specific water quality standards in waters that contain a substantial amount of wastewater effluent, but reinforces the need for regulators to scrutinize the composition of models, their thermodynamic and biotic ligand parameters, and the limitations of those parameters.

Diel variation of selenium and arsenic in a wetland of the Great Salt Lake, Utah

Abstract Diel (24-h) changes in Se and As concentrations in a freshwater wetland pond bordering the Great Salt Lake (GSL) were examined. Selenium concentrations (filtered and unfiltered) changed on a diel basis, i.e., were depleted during early morning and enriched during daytime over August 17–18. During the May 24–25, 2006 and September 29–30 diel studies, no significant 24-h trends were observed in Se concentrations compared to August, which showed daily maximums up to 59% greater than the daily minimum. Both filtered and unfiltered As concentrations also varied on a diel cycle, with increased concentrations during early morning and decreased concentrations during daytime. Filtered As concentrations increased 110% during the May 24–25, 2006 diel study. Selenium varied in phase with pH, dissolved O2 (DO), and water temperature (Tw) whereas As varied opposite to Se, pH, DO and Tw. Changes in pH, DO and Tw showed a direct linear correlation (r = 0.74, 0.75, and 0.55, respectively) to filtered Se. Also pH, DO and Tw were inversely correlated to filtered As concentration (r = −0.88, −0.87, and −0.84, respectively). Equilibrium geochemical speciation and sorption models were used to examine the potential oxidation state changes in Se and As, and sorption and desorption reactions corresponding to the observed 24-h variations in pe and pH. In this wetland it was postulated that diel Se variation was driven by sorption and desorption due to photosynthesis-induced changes in pH and redox conditions. Diel variations of As were hypothesized to be linked to pH-driven sorption and desorption as well as co-precipitation and co-dissolution with mineral phases of Mn.

Leaching characterisation and geochemical modelling of minor and trace elements released from recycled concrete aggregates

The pH dependent release of Cd, Cr, Cu, Mn, Mo, Ni, Pb, V and Zn from different recycled concrete aggregate samples was determined. Geochemical speciation modelling was applied on the concentrations of Cu, Cr, Mo and Ni in the leachates in order to predict the measured concentrations and the specific release mechanisms. The model was able to reproduce the characteristic pH dependent release patterns for these elements and reasonable to sometimes excellent matches between the predicted and measured concentrations were achieved. Binding of Mo and Cr as oxyanions (MoO 4 2− and CrO 4 2−) to ettringite was modelled with fair agreement for Cr only. For Cu and Ni, the predicted and measured concentrations agreed well for the partly carbonated sample at high alkaline pH (11–13). The importance of complexation to humic substances was also shown in samples derived from construction debris.

Antimony speciation and contamination of waters in the Xikuangshan antimony mining and smelting area, China

Water samples from Xikuangshan (China), the world largest antimony (Sb) mine with a Sb mining and smelting history of more than 200 years, were analyzed. These water samples ranged from stream water in the vicinity of the mining and smelting area that received seepage from ore residues to the underground mine-pit drainage. The concentrations of total Sb, Sb (III) and Sb (V) of the samples were determined by HPLC-ICP-MS. In addition, water pH and concentrations of major cations and anions were analyzed. All 18 samples demonstrated total Sb concentrations with ppm levels from 0.33 ppm to 11.4 ppm, which is two to three orders of magnitude higher compared to the typical concentration of dissolved Sb in unpolluted rivers (less than 1 ppb). This is probably the first time that such high Sb contents have been documented with complete environmental information. Distribution of total Sb and Sb species was investigated, taking into account the respective local environment (in the mining area or close to the smelter, etc.). Sb (V) was the predominant valence in all 18 samples. Only trace levels of Sb (III) were detected in 4 of the 18 samples. Geochemical speciation modeling showed the dominant species was Sb(OH)(6)(-). It is also probably the first time that such high Sb contents have been documented in the natural environment with Sb speciation distribution information. Several potential oxidation pathways are also discussed that might have facilitated the oxidation of Sb (III) in the natural environment. Signs of intoxication were observed among local mine workers with extensive exposure to different forms of Sb for a long period of time.

Impacts of Metal Contamination in Calcareous Waters of Deûle River (France): Water Quality and Thermodynamic Studies on Metallic Mobility

To evaluate adverse impacts of metal pollution originating from smelting activities on the aquatic ecosystem of Deule river in northern France, water samples were collected from five selected stations along a contaminated region of this river (during two surveys: April–June 2005 and April–May 2007). All samples were analysed using inductively coupled plasma (ICP) atomic emission spectroscopy and/or ICP-mass spectrometry. Both the concentrations of dissolved and particulate elements were determined, and analytical data were compared with national and international water/particle quality guidelines as well as with some values reported in the literature for polluted rivers. For all the metals studied (i.e. Cd, Cr, Cu, Mn, Ni, Pb and Zn), our investigations showed that the effects of the dissolved phase on this aquatic medium were weak, according to water quality status established by US Environmental Protection Agency, USEPA (1994, 1999). Conversely, the levels of metals in suspended particulate matter were found to be much higher than local background contents and natural reference levels in French catchments. These levels were further quantified as “serious” contamination, i.e. above the “red” range that was previously elaborated by most existing metal-contamination scales in French basins of similar geology. The affinity of these metals for the particulate phase in Deule waters follows the order: Cd >Cr > Pb > Zn = Mn > Cu > Ni. The trace metals released from anthropogenic activities were found to be partly bound to the reactive particulate phase, calcite, which is sensitive to physico-chemical variations occurring in the river ecosystem. To appraise the risk of ecotoxicity by metals, predictions on the ability to release metallic pollutants from calcite into waters were made successfully by testing three equilibrium geochemical speciation models (JCHESS, VISUAL MINTEQ and WINHUMIC) in which soluble organic matter was taken into account. Calculations showed that metal–water–calcite systems in Deule River are close to thermodynamic equilibrium with generation of solid solutions, MeαCa1-αCO3, by (co)precipitation and/or adsorption reactions. On the basis of results mentioned here, more measurements of river chemistry and assessments of predictive capabilities of chosen water-quality guidelines with time would be developed in aquatic and calcareous areas for controlled dredging operations or other treatment engineering works.

CO 2 distribution in groundwater and the impact of groundwater extraction on the global C cycle

Growing population and wealth, agricultural expansion, changing land use, and mechanized irrigation increase the demand on water resources. Groundwater accounts for about 20% of global water use, with agriculture the largest consumer. Groundwater CO 2 partial pressures are typically ∼ 10–100 times higher than atmospheric, so CO 2 degassing is an unavoidable consequence of groundwater extraction. For regional studies, very good estimates of groundwater CO 2 in clastic aquifers can be calculated for temperate-climate regions from: log 10 ( p CO 2 ) = log 10 ( HCO 3 − ) − pH + 7.749 where the constant is the sum of the negative logarithm (base 10) of the Henry's Law constant for CO 2 and first association constant for H 2CO 3 at 13 °C, and titration alkalinity can be substituted for activity of HCO 3 −. Groundwater CO 2 is not uniformly distributed in groundwater, being most variable near the water table, lowest at intermediate depth, and highest in deep aquifers where non-potable water is typical. Geochemical speciation modeling is required to assess CO 2 released when groundwater equilibrates with the atmosphere. A suite of potable water types were modeled for this purpose, with the result that current groundwater production is estimated to release ∼ 0.01 to 0.03 Pg C year − 1 , similar to CO 2 from volcanic emissions and ∼ 200 times less than other human-sourced CO 2 emissions. Determination of dissolved CO 2 depends on accuracy of pH measurements: CO 2 released due to groundwater use may be underestimated if reported pH measurements do not represent in situ pH.

Release of major elements from recycled concrete aggregates and geochemical modelling

The pH dependent leaching characteristics were assessed for different types of recycled concrete aggregates, including real construction debris and crushed fresh concrete samples prepared in laboratory. Carbonation effects were identified from the characteristic pH dependent leaching patterns for the major constituents Al, Ca, Fe, Mg, Si and SO 4 2–. The original particle size ranges were different for the samples investigated and this factor influenced the cement paste content in the samples which in turn controlled the leachable contents. Cement paste contents for concrete samples with fine particle size fractions (0–4 mm) were found to be higher than the originally present amount in the hardened concrete. Geochemical speciation modelling was applied over the entire pH range using the speciation and transport modelling framework ORCHESTRA, for which mineral saturation, solution speciation and sorption processes can be calculated based on equilibrium models and thermodynamic data. The simulated equilibrium concentrations by this model agreed well with the respective measured concentrations. The main differences between the fresh and aged materials were quantified, described and predicted by the ORCHESTRA. Solubility controlling mineral phase assemblages were calculated by the model as function of pH. Cement hydrate phases such as calcium silicate hydrate, calcium aluminate hydrate (AFm and AFt) and hydrogarnet were predominating at the material pH. The concentration of carboaluminates was found to be strongly dependent on the available carbonates in the samples. As the pH was decreased these phases decomposed to more soluble species or precipitates were formed including iron- and aluminium hydroxides, wairakite and amorphous silica. In the most acid region most phases dissolved, and the major elements were approaching maximum leachability, which was determined by the amount of cement paste.

Proton Binding Properties of Humic Substances Originating from Natural and Contaminated Materials

Humic substances (HS) are ubiquitous organic constituents in soil and water and can strongly adsorb metal contaminants in natural and waste environments. Therefore, understanding and modeling contaminant-HS interactions is a key issue in environmental risk assessment. Current binding models for HS, such asthe nonideal competitive adsorption (NICA)-Donnan model, are developed and calibrated against natural organic matter from soils and surface waters. The aim of this study is to analyze the proton binding properties of humic and fulvic acid samples originating from secondary materials,waste materials and natural samples in order to assess whether the charge development of these HS can be described with generic NICA-Donnan parameters. New proton binding parameters are presented for HS isolated from several natural and contaminated (waste) materials. These parameters are shown to be similar to those of HS originating from natural environments, suggesting that the NICA-Donnan model and generic binding parameters are adequate to describe proton binding to HS in both natural and contaminated materials. These findings widen the range of environments to which the NICA-Donnan model can be applied and justify its use in geochemical speciation modeling of metal mobility in contaminated (waste) materials.

Toxicity and metal speciation characterisation of waste water from an abandoned gold mine in tropical northern Australia

The decommissioned Mount Todd gold mine, located in the wet–dry tropics of northern Australia, consists of a large waste water inventory and an acid rock drainage problem, which has the potential to impact upon freshwater ecosystems of the Edith River catchment. The toxicity of retention pond 1 (RP1) water was determined using six local freshwater species (duckweed, alga, cladoceran, snail, hydra and a fish). RP1 water was very toxic to all species, with the percentage dilution of RP1 water inhibiting 10% of organism response (IC 10), or lethal to 5% of individuals (LC 5), ranging from 0.007 to 0.088%. The percentage dilution of RP1 water inhibiting 50% of organism response (IC 50), or lethal to 50% of individuals (LC 50), ranged from 0.051% to 0.58%. Based on chemical analyses and geochemical speciation modelling of the test waters, Cu, Zn and Al were the most likely toxic components at acidic dilutions (i.e. ⩾1%), while Cu and Zn were the most likely toxic components at 0.1% RP1 water, where pH was 6.5. Species sensitivity distributions (SSDs) were used to predict dilutions of RP1 water that would protect or unacceptably affect the downstream aquatic ecosystems. A dilution ratio of 1 part RP1 water to 20 000 parts Edith River water (0.005% RP1 water) was calculated to be required for the protection of at least 95% of species. This information can be used in conjunction with field chemical and biological data to better predict the ecological risks of RP1 waste water downstream of the Mount Todd mine.

Phosphorous concentration, solubility and species in the groundwater in a semi-arid basin, southern Malayer, western Iran

In areas of intensive crop production, continual phosphorous (P) applications as P fertilizer and farmyard manure have been made at levels exceeding crop requirement. As a result, surface soil accumulations of P have occurred to such an extent that loss of P in surface runoff and a high risk for P transfer into groundwater in concentrations exceeding the groundwater quality standard has become a priority management concern. Phosphorous content of groundwater was determined in order to examine dissolved P concentration and species in the groundwater and mineral solubilitiy in a semi-arid region of southern Malayer, western Iran. The speciation for P in groundwater was calculated using geochemical speciation model PHREEQC. The concentration of total P in the groundwater (0.01–2.56 mg P l−1) and estimated concentrations of HPO42− (49.5–89%), H2PO4− (1.5–17.3%), CaHPO4+ (5.7–36.1%), and CaPO4− (1.4–12.2%) varied considerably amongst the groundwater. Results suggest that the concentration of P in the groundwater could be primarily controlled by the solubility of octacalcium phosphate and β-tricalcium phosphate. Large amounts of P fertilizer, inadequate management of P fertilization, and low irrigation efficiency, coupled with sandy soils in some parts of the study area could be mainly responsible for the greater P in the groundwater. In general, the greater the dissolved P concentration in the groundwater, the closer the solution was to equilibrium with respect to the more soluble Ca-phosphate minerals. The groundwater P content could be potentially used to identify areas where management approaches, such as P applied and crop type planted, could be adjusted to different types of soils, geology and topography.

Effects of water chemistry variables on gill binding and acute toxicity of cadmium in rainbow trout ( Oncorhynchus mykiss): A biotic ligand model (BLM) approach

This study investigated the short-term (3 h) cadmium binding characteristics of the gills, as well as the influence of various water chemistry variables [calcium, magnesium, sodium, pH, alkalinity and dissolved organic carbon (DOC)] on short-term gill accumulation and acute toxicity of cadmium in juvenile freshwater rainbow trout. The cadmium binding pattern revealed two types of cadmium binding sites in the gill: (i) saturable high affinity sites operating at a low range of waterborne cadmium concentration, and (ii) non-saturable low affinity sites operating at a higher range of cadmium concentration. Among the water chemistry variables tested, only calcium and DOC significantly reduced both gill accumulation and toxicity of cadmium. Interestingly, alkalinity (15–90 mg L − 1 as CaCO 3) did not influence the gill cadmium accumulation but a significant increase in toxicity was recorded at a higher alkalinity level (90 mg L − 1 ). Affinity constants (log K) for binding of competing cations (Cd 2+ and Ca 2+) to the biotic ligand and for binding of Cd 2+ to DOC were derived separately from the 3 h gill binding tests and the 96 h toxicity tests. In general, the values agreed well, indicating that both tests targeted the same population of high affinity binding sites, which are likely Ca 2+ uptake sites on the gills. These parameters were then incorporated into a geochemical speciation model (MINEQL+) to develop a biotic ligand model for predicting acute toxicity of cadmium in trout. The model predictions exhibited a good fit with the measured toxicity data except for high alkalinity and pH.

Characterization of Untreated and Neutralized Bauxite Residue for Improved Waste Management

Alumina refineries generate large volumes of bauxite residue daily, and as such, the storage, treatment, and reuse practices for residue are receiving increasing attention as refineries strive to reduce the potential environmental impact of their operations. To improve management decisions in the selection of appropriate storage, treatment, and reuse practices, the leaching behavior of bauxite residue was characterized using a standardized pH dependence leaching test. Leaching data was modeled using a geochemical speciation program to determine which chemical processes are controlling bauxite residue leaching behavior. This approach showed that the nine residue samples examined behaved very similarly for most elements, despite being generated by different refineries that utilize bauxite from different sources. Geochemical modeling of the leach data helped identify the solubility controlling minerals and other release controlling factors, which proved mostly the same for this wide range of samples. Residue treatments such as carbonation and seawater neutralization did affect the leaching of some elements, resulting in a change in the leaching behavior of the treated material compared with the untreated sample. Using geochemical speciation modeling, the changes were largely explained; hence, this approach, aimed at understanding the geochemical phases controlling release, provides a sound basis for waste management decisions in a wide range of storage and reuse scenarios.

Monitoring and Modeling of Sand-Bentonite Cover for ARD Mitigation

This paper deals with field measurements and hydraulic, oxygen transport and geochemical speciation modeling undertaken to evaluate the performance of a sand-bentonite test cover overlying a 20% sloping waste rock platform. A pit run (gravelly sand) layer protected the sand-bentonite layer. The study site was the Whistle Mine near Capreol, Ontario, Canada. The purpose of the study was to evaluate a number of test covers and select a final cover for the decommissioning of 7 million tonnes of acid-generating waste rock at the site. The sand-bentonite test plot and a control plot consisting of waste rock without cover were monitored over 3 years for water content, suction, soil temperature, gaseous oxygen concentrations, and water percolation. Air temperature, rainfall, snow pack and potential evaporation were also monitored. Finite element modeling showed very good agreement between modeled and measured cumulative precipitation, daily potential evaporation and cumulative evaporation, and to a lesser extent, the cumulative water percolation through the test cover. Due to construction difficulties in the field, the back of the waste rock platform was not covered with the test cover. This resulted in oxygen ingress from the back side of the waste rock. Oxygen transport modeling showed that if the entire waste rock pile had been covered, the daily oxygen flux would have been reduced by 90% to only 0.003 g/m2/day. Such low oxygen flux would minimize sulphide oxidation and hence acid generation in the waste rock. Aqueous equilibrium speciation modeling suggested that the concentrations of sulphate $$\left( {{\text{SO}}_{\text{4}}^{{\text{2 - }}} } \right)$$ , iron (Fe), and aluminum (Al) in percolate water in contact with waste rock were controlled by secondary minerals such as gypsum, alunite, and ferrihydrite.

Caracterização da solução de solos do bioma cerrado sob pastagens

The aim of the present work was to characterize the soils solution and to examine Al’s speciation in soils under pasture in Brazilian Cerrado region. The soils used in this study were collected in the space between the towns of Goiânia, GO and Barra do Garcas, MT, to the margins of GO – 060 and BR – 154 highways. For the collection of soil solutions it was used a special equipment built with a PVC tube whose inferior extremity was coupled to a porous tip of special ceramic. To quantify the aluminum ionic species, two methods were used: chemical method of “ aluminon “ and the method WHAM (geochemical speciation model). The results allowed to conclude that the predominant aluminum ionic species varied in function of soil type, pH and concentration of NO 3- in the soil solution. More abundant Al’s species in the soils were Al-M.O., Al 3+ and Al(OH) 4- , in this order.

Inclusion of Some Aspects of Chemical Behavior of Unsaturated Soil in Thermo/Hydro/Chemical/Mechanical Models. I: Model Development

This paper presents an investigation of the inclusion of some aspects of chemical behavior within a model of coupled thermo/hydro/chemical/mechanical behavior of unsaturated soils. In particular, multicomponent reactive chemical transport behavior is addressed. The chemical transport model is based on the advection/dispersion/reaction equation, while geochemical reactions are considered via coupling with an established geochemical speciation model. A numerical solution of the governing differential equations is achieved by the use of the Galerkin-weighted residual method for spatial discretization and an implicit backward Eulerian finite-difference method for temporal discretization. The solution of the geochemical reactions is achieved externally to the main solution procedure. Coupling between the chemical transport and geochemical models is achieved via the implementation of both sequential iterative and sequential noniterative techniques. Three application problems are then presented to demonstrate the capability of the coupled model.

The effect of operating variables on chelant-assisted remediation of contaminated dredged sediment

The paper shows the results from a number of lab-scale washing treatments using the four chelating agents EDTA, NTA, citric acid and [S,S]-EDDS aiming at the remediation of a real heavy metal-contaminated sediment. Investigation of the influence of chelant type and concentration as well as solution pH was the major focus of the work. The analysis of speciation of metals and chelating agents in solution was carried out through geochemical speciation modelling in order to identify the optimal conditions for the washing process as well as to evaluate the competition phenomena of metal–chelant complexes in solution. The major competing cations were found to be Ca above all and Mg under specific conditions. Among the investigated chelating agents, EDDS appeared to be less affected by competition by major cations while ensuring adequate heavy metal extraction efficiencies. For a 1:1 chelant/metal ratio, the following ranking was observed: EDDS > Cit > NTA > EDTA for As, EDDS > NTA ≅ EDTA ≫ Cit for Cu, EDDS ≅ EDTA ≅ NTA > Cit for Zn, EDTA > NTA > EDDS > Cit for Pb at pH 5 and EDTA ≅ EDDS ≅ NTA ≫ Cit for Pb at pH 8. For a 10:1 chelant/metal ratio geochemical modelling indicated that at the equilibrium the extracting solutions were dominated by the free form of the chelating agents, indicating the inability of such species to complex trace metals due the strong interactions existing between heavy metal ions and sediment constituents.

Identification of Feedback in Pollutant Pathway Models

In many studies involving problem substances several pathways through the various compartments of the environment are relevant. In order to rank different pathways or to evaluate mitigation measures, numerical modeling can be an appropriate tool. Global, regional, or local compartment models, foodweb models, transport dispersion models, and geochemical speciation models have common features. At several levels (compartments, processes, species) such models can be characterized by directed graphs. Using graph-theoretical results a criterion for feedback as a relevant model property is formulated. If there is feedback within a model, phenomena are usually more complex, which has to be taken into account by numerical approaches. This places demands on computer resources. The graph-theoretical approach is illustrated on mercury as an example problem component.

English

A geochemical study was completed as part of an Environmental Assessment Report for De Beers Canada Inc. Snap Lake diamond mine located in the Canadian Northwest Territories. The deposit will be mined using underground methods and consists of a diamond bearing planar kimberlite dyke dipping at about 15 degrees, hosted in metavolcanic and granite rock. Processing will include grinding of the kimberlite ore and a gravity separation circuit on this ore which will result in processed kimberlite waste including a coarse fraction and a finer fraction which will be used to produce a cemented paste backfill material. The cemented paste composed of processed kimberlite, dilution rock, and cement is thickened to a paste-like consistency and will be used to fill the mine voids. The study discussed in this paper was completed to evaluate potential leachate chemistry of the alkaline cemented paste backfill material slated for use underground. The laboratory test program included solids testing, short-term leach testing, and longer-term kinetic testing on a variety of cemented paste blends and additives. Results show that the pH of the leachate remained alkaline for subaqueous test cells and decreased over time for sub-aerial test cells. Geochemical speciation modeling using PHREEQC that was completed to further evaluate leachate chemistry for site specific conditions indicated probable solubility constraints due to secondary mineral precipitation for parameters calcium, chromium, manganese and nickel.