Chelation alkaline

EDTA Chelates alkaline earth and heavy metals 0.005-0.01% w/v antimicrobial activity synergy Often used in combination with other antimicrobial preservatives, and other antioxidants based on their synergy... 

One strategy for avoiding the sludge problem is to use non-chelate process solutions wherever feasible. Non-chelate alkaline cleaners are available, as are non-chelate etchants... 

Properties Wh. powd. dissolves readily in water chelates alkaline earth cations but not toxic heavy metal ions m.w. (174.15)n Toxicology May be harmful by inh., ing., or skin absorption may cause eye/skin irritation TSCA listed... 

Phosphorylated chitosans (12.255a) may be used for chelating alkaline earth cations or stabilising bleaching agents. Chitins of type (12.255b) are reported to improve the textile properties of co-spun alginate fibres [21]. 

The sulfur atom of the thiocarbonyl group is a good nucleophile, and reaction between benzyl bromide and l-(2-thiazolyl)thiourea yields the isothiouronium salt (496). The sulfur atom may also be engaged in a chelate, as exemplified by the Cu chelate of 2-thioureido-4-methylthiazole (491). These chelates with metal ions were thoroughly studied in acidic, neutral, and alkaline media for 66 metal ions in order to define their analytical use. They are formed in the molar ratio of 1 2 for metal II compounds (498). 

Salt Formation and Metal Chelation, Most a-ainiao acids form salts in alkaline and acidic aqueous solutions (88). For example, a-amino acids form inner complex salts with copper. 

Further Preparative Reactions. When pulps are to be used in the production of materials that do not retain the original fiber stmcture, such as rayon or ceUulose acetate film, the lignin, hemiceUulose, and other components must be reduced to the lowest possible concentrations. A surfactant (ionic or nonionic) is often added during a hot, weakly alkaline extraction step after chlorination. Another approach, sometimes used in addition to the surfactant step, is to treat the pulp with 6—10% NaOH after most of the oxidative bleaching is finished. This treatment removes most of the hemiceUulose. In most purification plants the final stage includes use of sulfuric acid chelators are optional. 

The more stable the chelate, the higher the pM that it can maintain, and the higher the pH required to precipitate the metal hydroxide. From equation 22 it can be seen that the smaller the solubihty product ie, the more iusoluble the metal hydroxide, the higher the pM that a chelant must maintain to prevent precipitation. The stabiUty constant of the Fe(III)—EHPG complex (/2), is so large (10 ) that iron is not precipitated even ia strongly alkaline solutions. 

Another group of chelants that form stable chelates at high pH because of metal—alkoxide coordination are the sugar acids, such as gluconic acid [526-95-4] (1 )- Utility for this group is found in high alkalinity botde washes and other cleansers (19). 

The calcium chelate cements are limited to the use of a cavity liner. They may be placed directly over an exposed tooth pulp to protect the pulp and stimulate the growth of secondary dentin, or used as a therapeutic insulating base under permanent restorations. The high alkalinity and high solubihty of these materials prohibits use in close proximity to soft tissues or in contact with oral fluids. 

EDA reacts with formaldehyde and sodium cyanide under the appropriate alkaline conditions to yield the tetrasodium salt of ethylenediaminetetraacetic acid (24). By-product ammonia is removed at elevated temperatures under a partial vacuum. The free acid or its mono-, di-, or trisodium salts can be produced by the appropriate neutrali2ation using a strong mineral acid. This same reaction with other amines is used to produce polyamino acetic acids and their salts. These products are used widely as chelating agents. 

Palladium and Palladium Alloys. Palladium is used in telephone equipment and in electronics appHcations as a substitute for gold in specific areas. Palladium is plated from ammoniacal and acid baths available along with chelated variations as proprietary processes. One typical alkaline bath uses 8 g/L diammine-dinitropalladium, 100 g/L ammonium nitrate, and 10 g/L sodium nitrite. The pH is adjusted to 9—10 using ammonium hydroxide, and the bath is operated at 100 A/m at 50° C. If ammonium sulfamate, 100 g/L, is used in some baths to replace the nitrate and sodium nitrite salts, the bath is mn at lower temperature, 25—35°C, and a pH of 7.5—8.5. A palladium—nickel alloy, 75% Pd, is plated from a bath having 6 g/L palladium from the same salt, 3 g/L nickel from nickel sulfamate concentrate, and 90 g/L ammonium hydroxide. The bath is operated at 20—40°C with 50-100 A/m/... 

Quinoxaline-2,3-dithione (2,3-dimercaptoquinoxaline) (90) forms chelates with several transition elements and is used as a colorimetric agent for the detection and quantitative estimation of nickeT and also for the quantitative estimation of palladium. " Nickel gives a pink coloration with (90) in ammoniacal solution, and palladium an orange-red color in AA-dimethylformamide solution containing a little hydrochloric acid. Spectrophotometric studies of the chelate compounds of (90) with Ni(II), Co(II), and Pd(II) in alkaline solu-... 

Discussion. This method is based upon the formation of a fluorescent chelate between calcium ions and calcein [fluorescein bis(methyliminodiacetic acid)] in alkaline solution.29 The procedure described below30 has been employed for the determination of calcium in biological materials.31 ... 

Where a stable, passivated magnetite film exists, there is little risk of corrosion when using these products, and under normal alkaline boiler conditions (above a pH of 10.0), the chelation of ferric iron [Fe(OH)3, Fe203, Fe304] does not take place (so the protective magnetite film is not disrupted). 

NOTE It is also apparent that the ferric ion (Fe3+) should chelate most readily. In practice, however, under strongly alkaline conditions, the preferred reaction is to instantaneously form ferrous hydroxide and then to slowly revert to ferric hydroxide (competing anion effect). 

Optimum chelation pH level is 11.0 to 11.2. This corresponds to a P alkalinity in the boiler of approximately 300 to 500 ppm CaC03. The lowest practical caustic alkalinity is 100 ppm. 

If the alkalinity is too low, iron corrosion may take place. If the alkalinity is too high, there is a further competing anion effect, with magnesium precipitated as Mg(OH)2, rather than chelated. 

Where an alkaline EDTA cleaning program is employed, hydrazine sometimes is added to help keep the chelated iron in the ferrous state and prevent corrosion of exposed steel. Under very exacting circumstances, such as removing iron oxides from nuclear powered SGs, triammonium EDTA together with 0.5 M hydrazine may be employed, at a pH of 7 and a temperature of 200 °F (93 °C). 

---