Cadmium complexes phosphates

Nickel halide complexes with amines give mixtures of linear polymer and cychc trimers (30). Nickel chelates give up to 40% of linear polymer (31). When heated with ammonia over cadmium calcium phosphate catalysts, propargyl alcohol gives a mixture of pyridines (32). 

Fig. 4. Absorption spectra of thionein (Kagi and Vallee, 1961). Absorption spectra of metallothionein (A), thionein (A, B), and cadmium thionein (B). Difference spectra of cadmium and zinc thionein (C), and the cadmium and zinc complexes of 2-mercaptoethanol (D). In B, Cd " was added to 6 X 10 M thionein (0), the numbers (1-4) identifying the spectra also represent the multiples of the increments of Cd++ (5 X 10 M). In D, 6.8 X 10 M 2-mercaptoethanol was added to 4 X 10 M ZnCb or 2 X 10 M CdCU as shown. The ejis of the zinc complex was 6.3 X 10. The C2S0 of the cadmium complex was 1.46 X 10. In A, B, and C the buffer was 5 X 10 Af phosphate and succinate, pH 6. In D, the buffer was 0.03 M Tris, pH 7.6.

In the case of ligands containing phosphoric groups (np), including simple phosphates and nucleotides, their contribution to the stability of cadmium complexes, , is given by equation (10) ... 

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

Free, ionic species of metals are at their highest concentrations at lower pH, so metals tend to be more bioavailable under these conditions.121128 At acidic pH, more protons are available to saturate metal-binding sites.99 For example, metals are less likely to form insoluble precipitates with phosphates when the pH of the system is lowered because much of the phosphate has been protonated. Under basic conditions, metal ions can replace protons to form other species, such as hydroxo-metal complexes. Some of the hydroxo-metal complexes are soluble, such as those formed with cadmium, nickel, and zinc, whereas those formed with chromium and iron are insoluble. 

Schnepfe [83] has described yet another procedure for the determination of iodate and total iodine in seawater. To determine total iodine 1 ml of 1% aqueous sulfamic acid is added to 10 ml seawater which, if necessary, is filtered and then adjusted to a pH of less than 2.0. After 15 min, 1 ml sodium hydroxide (0.1 M) and 0.5 ml potassium permanganate (0.1M) are added and the mixture heated on a steam bath for one hour. The cooled solution is filtered and the residue washed. The filtrate and washings are diluted to 16 ml and 1ml of a phosphate solution (0.25 M) added (containing 0.3 xg iodine as iodate per ml) at 0 °C. Then 0.7 ml ferrous chloride (0.1 M) in 0.2% v/v sulfuric acid, 5 ml aqueous sulfuric acid (10%) - phosphoric acid (1 1) are added at 0 °C followed by 2 ml starch-cadmium iodide reagent. The solution is diluted to 25 ml and after 10-15 min the extinction of the starch-iodine complex is measured in a -5 cm cell. To determine iodate the same procedure is followed as is described previously except that the oxidation stage with sodium hydroxide - potassium permanganate is omitted and only 0.2 ml ferrous chloride solution is added. A potassium iodate standard was used in both methods. 

Forrester Environmental Services, Inc., has developed a group of technologies for the stabilization of wastes containing heavy metals, such as lead, cadmium, arsenic, mercury, copper, zinc, and antimony. These technologies have been used in both industrial pollution prevention and remediation applications. One version of the technology involves the use of water-soluble phosphates and various complexing agents to produce a less soluble lead waste. This process results in a leach-resistant lead product. 

A structure determination of CdL(H20)5 3H20 (L = guanosine-5 -phosphate) reveals a cadmium ion octahedrally coordinated by live water molecules and the N-7 of the purine ring system (Cd—N = 2.37 A Cd—O = 2.24-2.34 A).568 Similarly, a structure determination of CdL2(H20)4 (L = 8-azahypoxanthinato) reveals octahedral cadmium bonded to N-7 of the purine anions and to four water molecules.569 Theophylline (83) is frequently used as a substitute for guanine (84) in model systems, and the complexes [CdI (RNH2)2(H20)2] (L = 83) have been described.570... 

The retardation of chloride and sulphate through complex formation with cadmium enabling the separation of anions of interest [28] to be carried out, was found to be unsuitable, as the high concentration of cadmium ions necessary to achieve the desired effect led to the loss of fluoride and phosphate (probably owing to precipitation). 

Raman spectral studies of the species MX(n" 2) (n = 2—4 M = Zn, Cd, or Hg X = Cl, Br, or I) in anhydrous tributyl phosphate have been reported.24 For the MX2 molecules, sufficient metal dihalide-solvent interaction exists to suggest bent X—M—X species with C2v rather than >ooh symmetry. The effect appears most marked for zinc(n) and least marked for mercury(n), which is in accord with the Lewis acidity sequence ZnX2 > CdX2 > HgX2. A similar analysis of the anionic MX3 complexes formed from a 1 1 mixture of LiX and MX2 again demonstrates solvent interaction, and a tetrahedral C3v species is indicated, rather than the planar structure found in the solid state. Studies involving the halogeno-complexes of zinc, cadmium, and mercury in DMSO and DMF have also been reported.25,26... 

The metallic soaps of barium, cadmium, lead, and calcium are commonly used as stabilizers. They are HCl acceptors, but their reaction products often cause cloudiness in clear formulations. Alkyl and aryl phosphates are often used with them to inhibit precipitation of insoluble chlorides. Tin complexes have also been used successfully. 

CAM] Caminiti, R., Nickel and cadmium phosphates in aqueous solution. Cation-anion complex formation and phosphate - H2O interactions, J. Chem. Phys., 77, (1982), 5682-5686. Cited on page 205. 

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