Dolomite acid reactions

Dolomite samples of 50-250 mg were micro-drilled from the polished stained slabs, care being taken to discriminate between cementation episodes. Several samples of disseminated dolomite were also extracted from porous sandstones adjacent to the pervasively cemented fractures. Sample powders were digested in 100% H3PO4 at 90°C using a Micromass Multiprep (single acid reaction) system, and purified CO2 was analysed on a Micromass-VG Prism III mass spectrometer. The reproducibility of multiple NBS-19 runs with the Multiprep system is 0.05 forfi C and 0.09 for 5 0. All data are reported as %o deviation from the PDB international standard, and are listed in Table 2. 

One of the processes for extracting zirconium from the mineral zircon (ZrSi04) is to fuse the mineral with limestone or dolomite. The reaction product disintegrates on cooling into powdered calcium silicate and coarse crystals of calcium zirconate (equation 12.7). The zirconate is dissolved in acid and converted into zirconium salts or zirconium oxide, much of which are converted into the corrosion-resistant zirconium metal [12.38]. 

Temperature. Acid reaction rate increases with temperature. At about 150°F, the reaction rate of HCl and limestone is about twice that at SOT. The reaction rate of HCl in limestone is faster than in dolomite up to about 250°F (or somewhat less). At higher temperatures, the rates of reaction in limestone and dolomite are equally fast. 

Sulfur dioxide emissions may affect building stone and ferrous and nonferrous metals. Sulfurous acid, formed from the reaction of sulfur dioxide with moisture, accelerates the corrosion of iron, steel, and zinc. Sulfur oxides react with copper to produce the green patina of copper sulfate on the surface of the copper. Acids in the form of gases, aerosols, or precipitation may chemically erode building materials such as marble, limestone, and dolomite. Of particular concern is the chemical erosion of historical monuments and works of art. Sulfurous and sulfuric acids formed from sulfur dioxide and sulfur trioxide when they react with moisture may also damage paper and leather. 

We can use reaction modeling techniques to test the conditions under which dolomite will react with hydrochloric acid to produce gas in the injection zones. 

To configure a model of the reaction of dolomite with 30 wt.% hydrochloric acid, we start REACT and enter the commands... 

Dolomite is dissolved by hydrochloric acid. Data at initial conditions give the concentration of acid, gmol/liter, and its rate of reaction, gmol/liter-sqcm-sec, when exposed to 30 sqcm of solid in one liter of solution (Lund et al, Chem Eng Sci 28 691,1973). Find the constants of a power law equation. 

Carbon dioxide has a dominant effect on the dissolution of carbonate minerals, such as calcite and dolomite (Table 2.1). If a carbonate mineral dissolves in water that is equilibrated with a constant source of CO, then the concentration of dissolved carbonic acid remains constant and high. However, when calcite dissolution is accompanied by consumption of carbonic acid and a continuous source of CO is not maintained, the reaction proceeds further to achieve equilibrium. 

Distilled water is fairly nonreactive and practically does not interact with carbonates or silicates, such as limestone dolomite and marl or granite, basalt, or sandstone. However, when enriched with C02, water turns into carbonic acid and can dissolve rocks by means of the reaction... 

Calcite and dolomite are the common carbonate materials of sedimentary (limestone, sandstone) and metamorphic (marble) rocks used as building stones. These materials are highly susceptible to attack by acid deposition and by the presence of atmospheric SO2 according to the following reactions ... 

The dissolution of dolomite, calcium magnesium carbonate, in hydrochloric acid is a reataion of particular importance in the acid stimulation of dolomite oil teseivoirsd The oil is contained in pore space of the carbonate material and must flow through the small pores to reach the well bore. In matrix stimulation, HCl is injected into a well bore to dissolve the porous carbonate matrix. By dissolving the solid carbonate the pores will increase in size, and die oil and gas will be able to flow out at faster rates, thereby increasing the productivity of tbe well. The dissolution reaction is... 

A porous structure with small pores uniformly distributed can be achieved chemically by evolution of gas with the mixed slurry followed by stabilization of the bubble structure. The gas must be formed by reaction between two evenly and finely dispersed substances. Also, the rate of reaction must be slow, particularly immediately after mixing, so that the gas-producing substances can be incorporated properly before a significant amount of gas has evolved. Otherwise, much of the gas is lost during the mixing step. Mixtures of carbonates with acids such as dolomite and sulfuric acid have been used. Stabilization of the mixture to prevent bubbles from rising to the surface can be... 

Separation of Sip4 by the Conway microdiffusion method is a slow process [2,3], The sample to be analysed (e.g., copper, aluminium, iron alloys, dolomite, titanium dioxide) is decomposed with acids in a polystyrene Petri dish to which hydrofluoric acid is subsequently added. The Sip4 evolved is trapped in NaOH solution, e.g., in another Petri dish placed beside. Both vessels are placed inside another, tightly closed, polystyrene vessel. To achieve quantitative separation of silicon, the reaction is carried out at 70°C for 18 h. 

Carbon and oxygen isotopic analyses were performed using the extraction method of McCrea (1950). Samples were weighed prior to reaction and the weight per cent of calcite was determined mano-metrically. Multiple extractions were attempted for samples containing significant mixtures of calcite, dolomite and/or siderite. Calcite gas was extracted after 2 h of reaction with 100% phosphoric acid at 25 °C dolomite gas was evolved at 25°C over 3 days of reaction siderite gas was evolved at 50°C and extracted after visible reaction had ceased (typically 2-3 days). Most of the gases were analysed on a Nuclide gas-source mass spectrometer a few were analysed on a VG Prism gas-source mass spectrometer. 

Four core samples were selected for carbon and oxygen isotope analysis following identification of the mineralogy under bulk-rock XRD. Only samples dominated by dolomite cement were chosen for isotope analysis, as identified by XRD (Table 3). The samples were crushed to a fine dry powder. Carbon dioxide was extracted from the powdered samples by reaction with 100% phosphoric acid at... 

On the other hand, the order of rate dependence of the dissolution of dolomite with respect to H + is fractional, as for many oxides and silicates, indicating more complex reactions at the mineral surface. A further elucidation of the origin of this fractional order requires a better knowledge of the surface properties of the mineral and of the protonation reaction of the various surface sites. Classic acid-base titration of the surface of carbonates is difficult to realize because of the high reactivity of these minerals and the complexity of the dissolved carbonate system. 

In mineral-reagent systems, surface precipitation has been proposed as another mechanism for chemisorption. The solubility product for precipitation and the activities of the species at the solid-liquid interface determine the surface precipitation process. Under appropriate electrochemical conditions, the activity of certain species can be higher in the interfacial region than that in the bulk solution and such a redistribution can lead to many reactions. For example, the sharp increase in adsorption of the calcium species on silica around pH 11 has been shown to be due to surface precipitation (Somasundaran and Anan-thapadmanabhan, 1985 Xiao, 1990). Similar correlations have been obtained for cobalt-silica, alumina-dodecylsulfonate, calcite/apatite/dolomite-fatty acid, francolite-oleate and tenorite-salicylaldoxime systems. The chemical state of the surfactant in the solution can also affect adsorption (Somasundaran and Ananthapadmanabhan, 1985). 

---