Barite Dissolution Research Articles

Correlation of the Pit Depth in Crystal Etching by Dissolution

A theoretically rigorous formulation relating the pit depth to dissolution time for crystal etching is presented and verified. The data of K. Dunn, E. Daniel, P. J. Shuler, H. J. Chen, Y. Tang, and T. F. Yen [J. Colloid Interface Sci.214, 427 (1999)] for surface dissolution of barite are analyzed and correlated accurately. It is shown that the empirically determined power law pit growth function of F. Hunkeler and H. Bohni [Corrosion, 37(11), 645 (1981)] conforms to a special solution of the present formulation and their empirically determined power law exponent of 1/2 is theoretically justified. In addition, the present study provides some insight into the mechanism of the crystal dissolution rate process and the variation of pit depth during dissolution-induced etching.

Dissolution of the barite (001) surface by the chelating agent DTPA as studied with non-contact atomic force microscopy

DTPA (diethylenetriaminepentaacetic acid) is a chelating agent widely used for removal of barium sulfate (barite) scale in the petroleum industry. In this paper we report ex-situ investigations of barite dissolution in deionized water and in 0.18 M DTPA aqueous solutions. Non-contact atomic force microscopy (NC-AFM) was used to observe dissolution on the BaSO 4 (001) cleavage surface. Dissolution was carried out at room temperature in a 10 ml reactor. Each sample was first etched in solution and dried before examination by NC-AFM. Dissolution on the BaSO 4 (001) surface took place via development of etch pits. In deionized water, triangular etch pits were observed on the (001) terraces at room temperature. And, zigzag shaped etch pits were found at the edges of steps. In DTPA solutions, etch pits on the (001) terraces were observed and these became deeper and longer with increasing time. The geometry of these etch pits was trapezoidal, and/or trapezohedral. To explain this characteristic morphology caused by dissolution we suggest that the active sites of one DTPA molecule bind to two or three Ba 2+ cations exposed on the (001) surface.

Mechanisms of Surface Precipitation and Dissolution of Barite: A Morphology Approach

Barite (BaSO4) was synthesized at normal pressure and room temperature by mixing sodium sulfate and barium chloride solutions by gentle flow (0.5 ml/min.). The well-formed rectangular and rhombohedral crystals with smooth faces formed from solutions with low degrees of supersaturation. Most precipitates became single crystals. We employed the scanning electron microscope (SEM) to observe barite dissolution by chemical agent diethylenetrinitrilopentaacetic acid. Molecular modeling was used to assist the interpretation of the surface reaction. A kinetic model for the pit growth (initial dissolution) on the surface was evaluated. With SEM microanalysis of barite and kinetic model of pit growth, important surface phenomena and mechanisms of dissolution can be hypothesized. Surface phenomena and composition are very important in barite dissolution. Experimental results suggest that the initial dissolution starts on the two lowest energy surfaces: (001) and (210), and that the etch pits are elongated in one direction on the (210) surface and formed cavities on the (001) surface. The simulated surface structures by molecular modeling can aid the interpretation the pit formation on those selected surfaces.

Barium-rich authigenic clinoptilolite in sediments from the Japan Sea—a sink for dissolved barium?

Exceptional barium-rich clinoptilolite, a heulandite-group zeolite, with Ba contents of up to 1.83 wt.% BaO occurs in Miocene sediments from the Yamato Basin of the Japan Sea (ODP Site 797). The clinoptilolites with highest Ba-concentrations occur directly below the base of the sulfate reduction zone, where pore water Ba concentrations are high due to the dissolution of biogenic barite. Downcore variations of the Ba content in clinoptilolites and pore water show that the formation of Ba-rich crystals at 299 m depth coincides with a decrease of the pore water Ba concentration. Thus, formation of Ba-rich zeolites seems to provide a sink for dissolved Ba, although the occurrence of authigenic barite near the base of sulfate reduction might also contribute to the depletion of pore water Ba. These findings show that the intrachannel cation content of authigenic clinoptilolite is not directly controlled by a mineralogical precursor, but seems to reflect the geochemical conditions of the surrounding pore fluids. The formation of Ba-rich clinoptilolites in a sulfate-depleted environment with elevated pore water Ba concentrations and the concurrent decrease of dissolved Ba in the pore fluids documents the mutual influence of pore water composition and mineral chemistry during diagenetic processes in marine sediments.

Multiple seawater-derived geochemical signatures in Indian oceanic pelagic clays

This paper reports a geochemical study of oceanic clays. Major and trace elements were analyzed on smectite-rich, clay size (<2 μm) samples, bulk sediments, and leachate residues from the Central Indian Basin. SrNd isotopes were also studied to investigate their geochemical evolution during transport in the water column, sedimentation, and diagenesis. The region is of special interest because the sedimentation records the interaction between the detrital supply from the Bengal Fan in the north and the biosiliceous input associated with the equatorial divergence in the south. The clay size fractions display extremely variable trace element contents, e.g., [Ba] = 100–5000 ppm, [Sr] = 20–200 ppm, Ce/Ce ∗ = 0.9–3.3, [Nd] = 10–50 ppm. Although in the argillaceous samples, clay size fractions have a similar trace element imprint to the bulk sediment, some major fractionations occur in the biosiliceous samples between the clay and the bulk sediment, especially for Sr and rare earth elements (REE). Three major components may account for the variable geochemical signatures of these pelagic clays. The first component (component A), already identified by Fagel et al. (1994), is characterized by a homogeneous geochemical signature (La N/Yb N = 1.03–1.05; Th/Ta = 12.8–21.1; Ba/Th ∼ 28) and a nonradiogenic Nd isotopic composition ( 143Nd/ 144Nd ∼ 0.511880): it traces a detrital Himalayan-derived origin. The two other components display a seawater-derived isotopic composition with global Sr ( 87Sr/ 86Sr ∼ 0.709060) and regional Indian Ocean Nd ( 143Nd/ 144Nd ∼ 0.512200) signatures. Both components are enriched in Sr and Ba (Sr ∼ 150 ppm, Ba/Th ∼ 500), and they are either enriched in light rare earth elements (LREE, e.g., Nd ∼ 50 ppm) in the argillaceous sediments (component B) or LREE-depleted (Nd < 20 ppm) in the biosiliceous sediments (component C). The frequent occurrence of micrometric (<5 μm) Sr-REE-Th enriched barite grains showing three major habits (rhombic, rounded, dendritic) suggests that these biologically-derived mineral phases had a major role in the genesis of components B and C. A strong clay-barite equilibration is deduced from the Post Archean Australian Shales PAAS-like REE patterns of these barites and the Ba enrichment of the clays. We suggest that it results from two successive mechanisms of exchange. First, at the top of the oxygen minimum zone, the microbial-induced decay of organic matter is proposed to trigger a series of trace element transfers between the various particulate-forming components (clays, barites, and decaying organic coatings). This is proposed as the origin of the clay component B: the barite-derived components (Ba, Sr) and the organic-derived positive Ce anomaly are imported to the clay particles while the PAAS signature of the clays is retained by the remaining barite crystals. Second, after settling, the barites are believed to partly dissolve and recrystallize, especially in the anoxic part of the sedimentary column. This diagenetic barite dissolution is proposed as the origin of the clay component C.

Dissolution of barite by a chelating ligand: An atomic force microscopy study

Atomic Force Microscopy (AFM) has been used to observe the dissolution of (001) cleavage surfaces of barite (BaSO 4) in deionized water and in solutions of DTPA (diethylene triamine pentaacetic acid), a synthetic metal-ion chelating agent. Experiments were carried out in situ in a fluid cell as well as in air on samples previously etched and dried. In water the principal dissolution features are etch pits bound by {210} faces. In DTPA, there is a different dissolution process which on an (001) surface results in the removal of layers that are half-unit cell thick (3.5 Å). Etch pits within each half-layer are bound by {110} and {100} faces and occur in two different orientations which are related by a 2 1 screw axis parallel to the c crystallographic axis. Only one pit orientation is found within each half-layer, and this orientation is determined by the position of the surface sulfate groups. The etch pit geometry suggests that the active ends of a DTPA molecule form bonds to Ba 2+ ions along [110] directions. Two concentrations of DTPA solutions were studied, 0.05 and 0.5 M. These concentrations are used in the development of commercial solvents for barite scale deposits in oil wells. In these experiments the 0.05 M DTPA solution was found to be considerably more reactive as a solvent than the more concentrated solution, suggesting that surface passivation of the barite occurs at high DTPA concentrations.

US Geological Survey research on the environmental fate of uranium mining and milling wastes

Studies by the US Geological Survey (USGS) of uranium mill tailings (UMT) have focused on characterizing the forms in which radionuclides are retained and identifying factors influencing the release of radionuclides to air and water. Selective extraction studies and studies of radionuclide sorption by and leaching from components of UMT showed alkaline earth sulfate and hydrous ferric oxides to be important hosts of radium-226 (226Ra) in UMT. Extrapolating from studies of barite dissolution in anerobic lake sediments, the leaching of226Ra from UMT by sulfate-reducing bacteria was investigated; a marked increase in226Ra release to aqueous solution as compared to sterile controls was demonstrated. A similar action of iron(III)-reducing bacteria was later shown. Ion exchangers such as clay minerals can also promote the dissolution of host-phase minerals and thereby influence the fate of radionuclides such as226Ra. Radon release studies examined particle size and ore composition as variables. Aggregation of UMT particles was shown to mask the higher emanating fraction of finer particles. Studies of various ores and ore components showed that UMT cannot be assumed to have the same radon-release characteristics as their precursor ores, nor can226Ra retained by various substrates be assumed to emanate the same fraction of radon. Over the last decade, USGS research directed at offsite mobility of radionuclides from uranium mining and milling processes has focused on six areas: the Midnite Mine in Washington; Ralston Creek and Reservoir, Colorado; sites near Canon City, Colorado; the Monument Valley District of Arizona and Utah; the Cameron District of Arizona; and the Puerco River basin of Arizona and New Mexico.

The kinetics of barite dissolution and precipitation in water and sodium chloride brines at 44–85°C

The dissolution rate of natural barite cleavage fragments was measured in deionized water and NaCl brines over the temperature range 44–85°C. Dissolution followed first-order kinetics, with an activation energy of 24.9 ± 10.1 kJ/mol. The observed insensitivity to stirring rate and low absolute value of the rate constant (extrapolated k at 25° C = 3.30 ± 1.31 × 10 −3 L/ m 2 s) indicated desorption rather than volume diffusion as the rate-determining step. The NaCl concentration had no effect on k up to 0.1 M. Barite growth from supersaturated aqueous solutions was also studied. Precipitation followed a second order rate law, k 25° C = 162 ± 65 L 2/ sm 2mol, E a = 22.0 ± 14.3 kJ/mol, and was not sensitive to pH variation. A different rate law is likely to apply at high supersaturations, where a change in secondary growth morphology was observed.

The behavior of barium in anoxic marine waters

The present day distributions of Ba in the water columns at three anoxic marine sites, namely the Cariaco Trench, Framvaren Fjord, and Black Sea, are presented. Dissolved Ba levels generally increase with depth, ranging from 45–85, 64–280, and 180–460 nM in surface and bottom waters for the three basins, respectively. Small maxima are observed in the vicinity of the in redox interface in both the Framvaren Fjord and Black Sea. Comparison of the dissolved and particulate Ba, Fe, and Mn distributions show that the maxima do not result from adsorption onto freshly precipitated Fe and/or Mn oxyhydroxides. As for the open ocean, Ba cycling in all three basins is dominated by its uptake, primarily in the form of barite, into particulate matter associated with productivity in surface waters, followed by its regeneration at depth or in the sediments. Microbiological activity near the redox interface promotes the breakdown of settling particulate matter and the release of barite just above the O 2 H 2S interface in the Black Sea, and most likely in the Framvaren Fjord, thus providing in part for the observed maxima. Dissolution of such barite in the marginal sediments of these basins probably also contributes to the maxima. Thermodynamic calculations show deep Black Sea Ba concentrations exceed saturation with respect to pure barite by at least a factor of 2. However, the uniformity of the deep water concentrations suggests thermodynamic control by some phase; it is likely that impurities, incorporated into barite during its rapid formation near the surface in microenvironments provided by decaying organisms, are responsible for the levels observed. Additional factors controlling the distributions of Ba in each basin are also discussed.

Water depth and diagenetic constraints on the use of barium as a palaeoproductivity indicator

Abstract Sediments underneath the high productivity areas of the coastal upwelling and equatorial divergence zones in the Pacific and Indian oceans are enriched in barium, and on this basis the barium content of the sediments has long been suggested as a potential palaeoproductivity indicator. Analyses of sediments from the Peru margin corroborate the pattern of enhanced barium accumulation in areas of high primary productivity in the deep ocean, but also show that this pattern cannot be extended to shallow-water deposits. Sediments from the Peru shelf lack any barium enrichment, whereas this element is significantly enriched in slope and basinal deposits in water columns deeper than 2000 m. This depth effect is further illustrated at Site 682 located in the rapidly subsiding Lima Basin. The Quaternary sequence deposited at water depths &gt;3000 m is enriched in organic carbon, opal and biogenic barium. The Miocene sediments, although deposited under highly productive waters associated with a coastal upwelling centre, do not show an enrichment in the barium record corresponding to the very high organic carbon and opal levels; a pattern that is consistent with deposition in shallow basins. In addition to the effect of water depth on the barium distribution, overprinting of primary signals can be observed in sediments from upwelling areas undergoing strong anoxic diagenesis. Microcrystalline barite is partly dissolved in intervals depleted in interstitial sulphate as shown for sediments from the Peru margin. Dissolution of barite in sulphate depleted intervals of deep water sections leads to high barium concentrations near the termination of the sulphate reducing zone, where downward sulphate and upward barium diffusion foster local barite precipitation in diagenetic fronts. The barium distribution in sedimentary oxic and suboxic environments at deep water depositional sites has a high potential as a palaeoproductivity indicator; however, barium accumulation as a proxy for ocean fertility should be used with caution in areas of varying water depths and in anoxic diagenetic environments where sulphate depletion undersaturates the interstitial waters with respect to barite.

Trace-element distribution across calcite veins: A tool for genetic interpretation

Profiles of Sr/Ca, Mg/Ca and Ba/Ca in two sets of calcite veins within chalks of Senonian age in the Judean Desert, Israel, were utilized to identify both the system in which the calcite vein crystallized and the source of the indurating solution. The Mg/Ca, Sr/Ca and Ba/Ca profiles in veins located at the Dead Sea Rift boundary were different from profiles in veins located away from the Rift boundary. Na/Ca distribution, on the other hand, was affected by a post-crystallization source in both localities. It is suggested that during the first stage of vein growth Mg/Ca, Sr/Ca and Ba/Ca profiles in the veins closer to the Rift boundary were affected by the dolomitized country rock. The Sr/Ca and Mg/Ca profiles in the veins are too high to be explained by a congruent dissolution of the country rock during the second stage of their growth. Therefore, it is suggested that the solution which precipitated the veins during their second stage of growth obtained its high trace-element content either from incongruent dissolution of the country rock or, more likely from intrusion of post-dolomitization Rift water. During the second stage of vein growth, the Ba/Ca profile in this type of veins was determined by partial dissolution of barite. In contrast to veins located at the Rift boundary, the Mg/Ca, Sr/Ca and Ba/Ca profiles in veins located away from the Rift boundary were mainly determined by the mode of calcite crystallization (i.e. open vs. closed system). It seems that trace-metal distribution across calcite veins in the Judean Desert can be related to epigenetic processes such as intrusion of Rift waters, as well as regional and local tectonic activities.

Groundwater chemistry and water-rock interactions at Stripa

Groundwaters from near surface to a depth of 1232 m in the Stripa granite have been sampled and analyzed for major and trace constituents. The groundwater composition consists of two general types: a typical recharge water of Ca-HCO 3 type (<300 m depth) and a deeper Na-Ca-Cl type (>700 m depth) of high pH (8–10) that reaches a maximum of 1250 mg/L in total dissolved solids (TDS). Intermediate depths show mixtures of the two types that are highly fracture-dependent rather than depth-dependent. Any borehole can vary significantly and erratically in TDS for either a horizontal or vertical direction. The general transition from Ca-HCO 3 type to Na-Ca-Cl type correlates with the depth profile for hydraulic conductivity that drops from 10 −8 m/s to 10 −11 m/s or lower. Thermomechanical stress (from heater experiments) clearly shows an effect on the groundwater composition that could be caused by changing flow paths, leakage of fluid inclusions or both. Dissolution and precipitation of calcite, fluorite and barite, aluminosilicate hydrolysis, and addition of a saline source (possibly fluid inclusion leakage) play the major roles in defining the groundwater composition. The low permeability of the Stripa granite has produced a groundwater composition that appears intermediate between the dilute, shallow groundwaters typical of recharge in a crystalline rock terrain and the saline waters and brines typical of cratonic shield areas at depth.

Dissolution of barite for the analysis of strontium isotopes and other chemical and isotopic variations using aqueous sodium carbonate

A simple procedure for preparing barite samples for chemical and isotopic analysis is described. Sulfate ion, in barite, in the presence of high concentrations of aqueous sodium carbonate, is replaced by carbonate. This replacement forms insoluble carbonates with the cations commonly in barite: Ba, Sr, Ca and Pb. Sulfate is released into the solution by the carbonate replacement and is separated by filtration. The aqueous sulfate can then be reprecipitated for analysis of the sulfur and oxygen isotopes. The cations in the carbonate phase can be dissolved by acidifying the solid residue. Sr can be separated from the solution for Sr isotope analysis by ion-exchange chromatography. The sodium carbonate used contains amounts of Sr which will affect almost all barite 87 Sr 86 Sr ratios by less than 0.00001 at 1.95θ of the mean. The procedure is preferred over other techniques used for preparing barite samples for the determination of 87 Sr 86 Sr ratios because it is simple, rapid and enables simultaneous determination of many compositional parameters on the same material.

The isotopic composition of western Canadian barites and the possible derivation of oceanic sulphate δ34S and δ18O age curves

Seventeen samples of stratiform barite hosted in Middle Cambrian to middle Mississippian marine sedimentary rocks of the western Canadian Cordillera were analyzed to determine their δ34S and δ18O values. Whereas some samples had isotopic values close to those for time-equivalent evaporites, others were clearly more enriched in the heavy oxygen and sulphur isotopes. Samples with isotopic values close to the evaporite curve were from very thick stratiform barites hosted mainly in organic-rich shales, and from thin and nodular beds hosted in organic-free sedimentary strata. All samples enriched in heavy isotopes were collected from thin or nodular deposits hosted in organic-rich sedimentary strata. Enrichment of barite in heavy isotopes can be achieved by a barite precipitation–dissolution process that cycles barium between oxygenated and reduced zones in either redox-stratified wet sediment, or sea water. This cycles requires barite to either settle from oxygenated sea water into more reducing water or to precipitate within or settle into wet sediment where Eh values are decreasing in situ during sediment buildup. Because all anomalously isotopically heavy barites are hosted in organic-rich strata, barite dissolution during this cycle likely occurs through the bacterial metabolism of organic matter and sulphate, during which sulphate with 16O and 32S is preferentially broken down. The main products of this bacterial activity are CO2 and H2S, which can react to form carbonates or pyrite or can escape from the system, resulting in a depletion of light isotopes from the remaining aqueous sulphate. Because thick deposits of barite hosted in organic-rich shale, unlike smaller deposits hosted in the same strata, do not show heavy isotopic enrichment, the main factor controlling isotope fractionation is likely the rate of barite precipitation relative to barite dissolution and reduction. The δ34S versus δ18O values for six samples of Upper Devonian rocks plot fall on a line with a slope of 2. The data and observations presented here and in published reports indicate that alteration of the isotopic composition of stratiform barite strongly favours enrichment in heavy isotopes with respect to coeval sea-water sulphate. It should be possible then, to construct a barite sulphate isotopic composition age curve by averaging the lower δ18O and δ34S values for samples of the same age.