Acid neutralization and metal mobilization in oil sands froth treatment tailings

This study focused on acid neutralization reactions and the effects of water composition on the release and mobility of metals from mine tailings. The aims of this study were to: investigate leaching of metals from neutral mine tailings, determine the factors responsible for metal leaching, and investigate potential metal filtering by the soil. Tailings and soil samples were collected from an iron mine and analyzed. Equilibrium thermodynamic data and metal fractionation were then used to predict precipitation/dissolution of minerals and ion adsorption/desorption. Three column experiments were designed. The first column was filled with tailings, while the second column contained tailings above a layer of soil; both were leached with distilled water as rainfall. The third column was packed with soil and percolated with synthetic groundwater. The results indicated that iron (Fe) and zinc (Zn) mobility are mainly controlled by precipitation–dissolution mechanisms, while sorption onto oxides and carbonates limit the mobility of copper (Cu) and nickel (Ni). Cadmium (Cd) and manganese (Mn) mobility are affected by both mechanisms. Water discharging from column 3 (soil washed with groundwater) contained high concentrations of dissolved metals, indicating that water composition played an important role in metal mobility. Buffering minerals like carbonates and hornblende, chlorite, and albite decreased acid generation.

Sorption, desorption, and leaching of metals in the sediments of the aquatic environment are paramount important in their bioavailability. Also, behavior of these metals in such sediments as the riverbed sediments is affected by the characteristics of the sediments such as grain size, pore size distribution, and pH of the medium. Four riverbed sediments with varying properties were artificially contaminated with cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn). Then, using leaching columns, they all were subjected to drying and wetting phases to study the competitive binding and release of metals. Sediment samples were collected from 0 to 10 cm depth of Abshineh and Ghareh Chai River during the dry season. Samples were spiked with 400 mg Zn kg−1, 200 mg Cu kg−1, 200 mg Ni kg−1, and 50 mg Cd kg−1 (dry weight equivalent) in plastic container and then after drying seated at a height of 10 cm in leaching column. Sediment columns were incubated at room temperature (22–24 °C) and leached with 10–20 pore volumes (PVs) with distilled water. The distribution of metals over different extractable fractions was evaluated before leaching. The four metals were separated into two classes according to their leachability. In the sediment columns that contained more clay, commonly mobile metals like Zn, Ni, and Cd that appeared to be rather immobile and commonly immobile metals like Cu were unexpectedly quite mobile. The observation that copper leachability was higher for the sediments with finer grain size and higher organic matter content indicates that pore size distribution, the presence of organically complexes, and colloidal particles, may have had major role in this mobility behavior of copper. The mobility of Zn and Cd are strongly governed by pH, where the mobility of Cd is typically much greater than Zn under acidic conditions. The metal addition caused the displacement of Ca, Mg, K, and Na their subsequent leachate from the spiked sediment columns. Despite the spiking of inorganic metals into the sediments and drying before leaching, the mobilization of metals with distilled water (to mimic rainwater) was small in the different sediments relative to the total amounts of each metal added. This would indicate that the major part of the added metals were likely to be bound in forms that exhibit a low potential for release to the environment and low bioavailability to organisms.

Acid neutralization mechanisms and metal release in mine tailings: a laboratory column experiment

Acid generation potential and kinetics of metal(loid) release from resuspended sulfidic mine waste

Mechanisms controlling acid neutralization and metal mobility within a Ni-rich tailings impoundment

Acid mine drainage (AMD), wherein acidic water is generated from pyrite-containing waste rock, can be mitigated by encapsulating pyritic waste rock with cover materials to restrict the inflow of oxygen and water. However, acidic water inevitably forms during the construction of waste rock dumps before applying cover materials. Considering that the presence of waste rock containing carbonate minerals contributes to acid neutralization, a mixture of carbonate minerals and pyritic waste rock can be utilized to reduce AMD generation before the completion of the cover system as a temporary management strategy. This paper examines waste rock management using blending scenarios. Kinetic NAG and column leaching tests were employed to evaluate the blending ratio necessary to prevent acidic water generation. Geochemical analyses were conducted on rock and leachate samples, including pH and temperature measurements, XRD and XRF analyses, and Ion Chromatography. Consequently, the pH and temperature measurement results obtained during the kinetic NAG test are valuable for expressing the balance between acid generation and acid neutralization by the mixture material. Furthermore, the column leaching test demonstrated that the pH of the leachate remained neutral when the acid generation and acid neutralization reactions were well balanced. Blending waste rocks is an effective method for AMD reduction during the construction of waste rock dumps.

Coastal reclamation has been carried out along the coastal areas near Shenzhen, China in a large scale since 1980s by dumping fill materials over the marine mud at the sea bottom. Usually the area to be reclaimed is drained first and some of the mud is air-dried for a few weeks before it is buried by fill. After reclamation, the terrestrial groundwater, which is relatively acidic and with high dissolved oxygen, gradually displaces the seawater, which is alkaline with high salinity. The changes in the burial conditions of mud and the properties of the pore water in the mud may induce the release of some heavy metals into the mud. Field survey confirms that the pH and salinity of the groundwater in the reclamation site are much lower than the seawater. Chemical analyses of mud and groundwater samples collected from the reclamation sites reclaimed in different years indicate that most of the heavy metals in the mud decrease gradually with time, but the heavy metals in the groundwater are increased. The release of heavy metals into pore water due to reactivation of heavy metals in the mud is of environmental concern. To understand why some of the heavy metals can be released from the mud more easily than others, a sequential extraction method was used to study the operationally determined chemical forms of five heavy metals (Cu, Ni, Pb, Zn, and Cd) in the mud samples. Heavy metals can be presented in five chemical forms: exchangeable, carbonate, Fe–Mn oxide, organic, and residual. Ni and Pb were mainly associated with the Fe–Mn oxide fraction and carbonate fraction; Zn was mainly associated with organic fraction and Fe–Mn oxide fraction, while Cu and Cd were associated with organic fraction and carbonate fraction, respectively. If the residual fraction can be considered as an inert phase of the metal that cannot be mobilized, it is the other four forms of heavy metal that cause the noticeable changes in the concentration of heavy metals in the mud. On the basis of the speciation of heavy metals, the mobility of metals have the following order: Pb (36.63%) > Cu (31.11%) > Zn (20.49%) > Ni (18.37%) > Cd (13.46%). The measured metal mobility fits reasonably well with the degree of concentration reduction of the metals with time of burial observed in the reclamation site.

Morphology, physicochemical properties, chemical composition of post-galvanized sewage sludge from Screw Factory in Łańcut, leachability and mobility of metals has been analyzed. The analyses with the use of scanning electron microscope with an adapter to perform chemical analysis of microsites (EDS) showed that the material is characterized by a high fragmentation and a predominant number of irregularly shaped grains. The sewage sludge is alkaline with a large loss of ignition (34.6%) and small bulk density (< 1 g/cm3). The EDS analyses evidenced presence of oxygen, silicon, calcium, chromium, iron and zinc in all examined areas, and presence of manganese and copper in selected areas indicating a non-uniform distribution of metals in the sewage sludge. Within one-stage mineralization and FAAS technique a predominant share of calcium, zinc and iron in terms of dry matter was recorded in the sewage sludge. The contents of Co, Cr, Cu, K, Mn, Ni and Pb in sewage sludge are below 1%. Evaluation of mobility and leaching of metals in sewage sludge was carried out by means of two parameters: accumulation coefficient of mobile fractions and leaching level related to the mass solubility of sewage sludge. The results indicate that the short-term or long-term storage of not inactivated post-galvanized sewage sludge can result in release of metals.

Influence of inorganic anions on metals release from oil sands coke and on toxicity of nickel and vanadium to Ceriodaphnia dubia

Surfactant-induced mobilisation of trace metals from estuarine sediment: Implications for contaminant bioaccessibility and remediation

The application of pH stat leaching tests to assess the pH-dependent release of trace metals from soils, sediments and waste materials

Sediment as the largest storage and resources of heavy metal plays an important role in the metal remobilisation and release. Continuous particulate matter in suspension increased the level and mobility of metals, of which poses a serious problem particularly to aquatic organisms. The purpose of this research is to investigate the fate and amount of contaminant released through sediment resuspension by using particle entrainment simulator (PES) with low turbulence intensity. The heavy metal release from sediment mixture of sand/silt/clay with percentage of 90/5/5, respectively was studied. In particular, the research paid attention to the contaminant release at the early resuspension stage (i.e. within 3 hr resuspension) by reviewing the metal releases of Zn, Cd and Pb in water column at five elevations from the bed of PES. Results showed that the concentration of remobilised heavy metal during resuspension event for Cd, Zn and Pb was in ranged of 0.034 to 0.139 mg/L, 0.014 to 0.071 mg/L and 0.007 to 0.029 mg/L respectively. The affinities of heavy metal release discussed in this study was Cd > Zn > Pb. Concentrations of the heavy metal fluctuated within the water column and have the lowest values at near bed. The highest concentration observed for Cd and Zn was at one integral length scale from the sediment bed and at t = 120 mins. Even at low turbulence intensity, the heavy metal release was still observed and is significant to the water quality.

A laboratory batch experiment was performed to evaluate the release of nutrients and heavy metals from a heavily polluted sediment under various pH and redox conditions and its implications on the various remediation methods. The sediments were equilibrated under various controlled redox (—200, 0, and 300 mV) and pH (5.0, 6.5, and 8.0) conditions. After attaining equilibrium, water samples were collected to determine the concentrations of NH4 +, PO4 3‐, Cd, Cu, Fe, Ni, Mn, Pb and Zn released. A decrease in pH and an increase in redox potential caused a substantial release of Cd, Cu, Pb, Ni, Mn and Zn. Soluble Fe, NHj and PO4 3‐ increased with a decrease in pH and redox potential. The results suggest that dredging and disposal of sediments may enhance the mobilization of enriched heavy metals in sediments due to the more acidic and oxidized conditions after exposure to the atmosphere.

Mineralogy and geochemistry of oil sands froth treatment tailings: Implications for acid generation and metal(loid) release

Mobility and toxicity of metals in sandy sediments deposited on land