Scale strontium sulfate

Occurrence. The principal strontium mineral is celestite, naturally occurring strontium sulfate. Celestite and celestine [7759-02-6] both describe this mineral. However, celestite is the form most widely used in Knglish-speaking countries. Celestite has a theoretical strontium oxide content of 56.4 wt %, a hardness of 3—3.5 on Mohs scale, and a specific gravity of 3.96. It is usually white or bluish white and has an orthorhombic crystal form. 

The scale may consist of calcium carbonate, barium sulfate, gypsum, strontium sulfate, iron carbonate, iron oxides, iron sulfides, and magnesium salts [943]. There are monographs (e.g.. Corrosion and Scale Handbook [159]) and reviews [414] on scale depositions available in the literature. 

A positive LSI means that scaling is favored a negative LSI means that corrosion is favored. It is desirable to keep the LSI near zero (or below) in the RO concentrate to minimize calcium carbonate scaling. This is usually accomplished by feeding acid to lower the pH or feeding an antisealant (see Chapter 8.2.3). Care must be given if sulfuric acid is used to adjust the pH, as this may exacerbate sulfate-based scales, such as calcium sulfate, barium sulfate, and strontium sulfate. 

Barium and strontium form sulfate scales that are not readily soluble. In fact, barium is the least soluble of all the alkaline-earth sulfates. It can act as a catalyst for strontium and calcium sulfates scale.4 Analyses of the ion product with the solubility constants for barium and strontium sulfates is necessary to determine the potential for scaling with these species. If the ion product (IP) for barium sulfate exceeds the solubility constant, scale will form. Note that in the case of strontium sulfate, if IP > 0.8Ksp, scaling is likely. However, the induction period (the time it takes for scale to form) is longer for these sulfate-based scales than it is for calcium carbonate scale. 

Calcium sulfate is a sparingly-soluble salt. As with barium and strontium sulfate, the potential to scale with calcium sulfate is high when the ion product exceeds 80% of the solubility constant. Antisealants or sodium... 

To illustrate the matrix damage problem in the reservoir and scale formation in production wells an application using the numerical code is presented. In this example, sulfate scaling occurs by mixing of injected water (seawater rich in sulfate and poor in Ca", Sr" and Ba ) with a connate water rich in Sr and Ba" cations. From this mixing strontium sulfate salt (SrSOj) and barite (BaS04) precipitations are expected. This kind of scaling is typical from the North Sea (Osborne et al., 1994) and also common in Campos Basin, Brazil (Silva et al., 2001). 

Synonyms Polyacrylic acid/hypophosphite copolymer, sodium salt Toxicology TSCA listed Uses Scale inhibitor for control of barium/strontium sulfate scale, oil field applies. boiler water additive (food contact) Regulatory FDA 21CFR 173.310 (1.5 ppm max.) Trade Name Synonyms Bellasol S29 f[BioLab Water Addit. http //www.wateradditives.com]... 

Maleic anhydride, polymer with ethyl acrylate and vinyl acetate, hydrolyzed scale inhibitor, barium/strontium sulfate Polyacrylic acid-co-hypophosphite, sodium salt... 

Strontium - Strontium sulfate (SrS04) has a minimum solubility in 40% phosphoric acid. SrS04 forms a scale in the heat exchangers of phosphoric add concentrators. An extremely thin film of this precipitate causes pronounced reductions in the capacities of such units 137]. 

Laboratory Screening Test to Determine the Ability of Scale Inhibitors to Prevent the Precipitation of Barium Sulfate and/or Strontium Sulfate from Solution (For Oil and Gas Production Systems)... 

Barium and strontium form sulfate scales that are not readily soluble. In fact, barium is the least soluble of all the alkaline-earth sulfates. It can act as a catalyst for strontium and calcium sulfate scales." Analyses of the ion product with the solubility constants for barium and strontium sulfates is... 

Calcium sulfate is a sparingly-soluble salt. As with barium and strontium sulfate, the potential to scale with calcium sulfate is high when the ion product exceeds 80% of the solubility constant. Antisealants or sodium softening to remove calcium can be used to control calcium sulfate scale. Calcium phosphate has become a common problem with the increase in treatment of municipal waste-water for reuse. Surface waters can also contain phosphate. Calcium phosphate compounds can also contain hydroxyl, chloride, fluoride, aluminum, and/ or iron. Several calcium phosphate compoimds have low solubility, as shown in Table 7.3. SolubiUty for calcium carbonate and barium sulfate are also shown by comparison. The potential for scaHng RO... 

Figs 9.9 and 9.10 can be used to obtain K, Pca and PaDc for the stability index. Similar indices may be used to predict bariiun sulfate or strontium sulfate or calcium sulfate deposition. If the product of concentration of Ca ions and SO4 ions exceeds the solubility products ( p) of CaS04, calcium sulfate would be precipitated. The solubility of calcium sulfate decreases with an increase in the temperature. CaCOj and CaS04 scaling cause major problems in plants and equipment encountering salt water. 

Deposition of inorganic scale may occur during well production. Depending on well conditions and produced water characteristics, different scale types may form. Often, scale formation is associated with a breakthrough of water production. Common scales include calcium carbonate, iron carbonate, calcium sulfate, barium sulfate, strontium sulfate, andiron sulfide. Combinations may also form. Figures 3-2 and 3-3 show well samples of calcium carbonate and iron scale, respectively. 

If the sample does not react in any of the above tests, then the scale is probably either barium sulfate or strontium sulfate, and a sodium carbonate fusion is necessary. Usually these samples are white. 

Remove the tube, cool in a beaker of cold water and stir occasionally. A yellow precipitate means the scale is strontium sulfate. (The yellow precipitate can be tested by a flame test. A red flame... 

Practical means of dissolving barium or strontium sulfate are not available. These hard scales can be removed by mechanical means, which is a time-consuming process. Mechanical removal of scale can create a disposal problem for the resulting waste material and possibly could result in contamination by naturally occurring radioactive materials (NORM). 

Sulfate scaling poses a special problem in oil fields of the North Sea (e.g., Todd and Yuan, 1990, 1992 Yuan et al., 1994), where formation fluids are notably rich in barium and strontium. The scale can reduce permeability in the formation, clog the wellbore and production tubing, and cause safety equipment (such as pressure release valves) to malfunction. To try to prevent scale from forming, reservoir engineers use chemical inhibitors such as phosphonate (a family of organic phosphorus compounds) in squeeze treatments, as described in the introduction to this chapter. 

Mixing of unlike brines can cause the precipitation of sulfates of barium, strontium, and calcium. This hard scale, which is a nuisance in oilfield flow lines, often can be explained by leaky casing. Soft scale, composed of calcium carbonate, usually is caused by the loss of dissolved carbon dioxide from the brine during pressure reduction. 

---