Phosphates and Arsenates

Fig. 3. Sorption of arsenate (ASO4) onto ferrihydrite or Al(OH)x in the presence of phosphate (PO4) or phosphate and malate (Mai) at 50% surface coverage of arsenate and at initial ASO4/PO4 molar ratio of 1.0 or 0.5. Arsenate and phosphate were added as a mixture (As04+P04 As04+2P04) or phosphate was added 24 hrs before arsenate (P04 before As04) or arsenate was added 24 hrs before phosphate (As04 before P04). Arsenate, phosphate and malate were added as a mixture (As04+ P04/Mal molar ratio of 1). The numbers in parenthesis indicate the effectiveness of phosphate in preventing arsenate sorption. From Del Gaudio (2005).

Bertrand Pelletier, 1761-1797. French chemist and pharmacist who investigated the arsenates, phosphates, and phosphides of many metals, studied the action of phosphorus on platinum, and devised new methods for making soap and refining metal for clocks. He served as inspector of the hospitals m Belgium. His son, Joseph Pelletier (1788-1842), and Joseph Caventou discovered quinine, cmehomne, strychnine, and brucine. See also ref. (89). 

See Graham, Researches on the Arsenates, Phosphates and Modifications of Phosphoric Acid, Phil. Trans., 1833, X23, 253. 

Large amounts of sulphates, thiosulphates, nitrites, arsenates, phosphates, and oxalates interfere with the test. 

It may be pointed out that if arsenite is also present it may be readily detected in the filtrate obtained by treating the original mixture of arsenate, phosphate, and arsenite with the magnesium nitrate reagent upon acidifying with 2m hydrochloric acid and passing hydrogen sulphide, an immediate yellow precipitate of arsenic(III) sulphide is produced. 

The apatite group minerals are hexagonal or pseudohexagonal monoclinic arsenates, phosphates and vanadates of generd formula A5(X04)3Z, where... 

Despite the fact that silicate-phosphate glasses showed some unexpected toxic influences, there are many other mixed anionic systems worthy of study. The borate-phosphate systems have been studied to a small degree. Some work has been done on sulfate-phosphate systems. Thilo s group studied the arsenate-phosphate and stibnate-phosphate chemistries in great detail, but very little applied work was done. This was probably a result of the mild toxicity of these systems. 

It is observed that anions based on milder Lewis acids are stable in organic solvents at room temperature and have been extensively investigated by workers in this field. Examples of these salts include lithium perchlorate and lithium borates, arsenates, phosphates, and antimonates. Following Xu [1], some examples of these salts are presented in Table 11.3, together with some of their basic physical properties also shown are their ion conductivity data in PC, and EC/DMC (1 1) the two solvents well studied by investigators in the area of lithium battery research. In general, carbonates and esters are more anodically stable while ethers are more resistant to cathodic decompositions [1]. Thus, solvents used in most commercial batteries are mixtures of solvents, plus some additives, in order to obtain various desirable properties their compositions are usually kept as proprietary information. 

SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHATE AND ARSENATE IONS BY MEANS OF IONIC ASSOCIATES OF CYANINE DYES WITH POLYOXOMETALATES... 

EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHATE AND ARSENATE USING IONIC ASSOCIATES OF POLYOXOMETALATES WITH BASIC DYES... 

A striking example of the importance of narrowing the focus in research, which is what the concept of the parepisteme really implies, is the episode (retailed in Chapter 3, Section 3.1.1) of Eilhard Mitscherlich s research, in 1818, on the crystal forms of potassium phosphate and potassium arsenate, which led him, quite unexpectedly, to the discovery of isomorphism in crystal species and that, in turn, provided heavyweight evidence in favour of the then disputed atomic hypothesis. As so often happens, the general insight comes from the highly specific observation. 

NaAs03 has an infinite polymeric chain anion similar to that in diopside (pp. 349, 529) but with a trimeric repeat unit LiAs03 is similar but with a dimeric repeat unit whereas /6-KASO3 appears to have a cyclic trimeric anion As309 which resembles the cyc/o-trimetaphosphates (p. 530). There is thus a certain structural similarity between arsenates and phosphates, though arsenic acid and the arsenates show less tendency to catenation (p. 526). The tetrahedral As 04) group also resembles PO4) in forming the central unit in several heteropoly acid anions (p. 1014). 

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. 

The most general method for the simultaneous analysis of oxyanions by gas chromatography is the formation of trimethylsilyl derivatives. Trimethylsilyl derivatives of silicate, carbonate, oxalate, borate, phosphite, phosphate, orthophosphate, arsenite, arsenate, sulfate and vanadate, usually as their ammonium salts, are readily prepared by reaction with BSTFA-TMCS (99 1). Fluoride can be derivatized in aqueous solution with triethylchlorosilane and the triethylfluorosilane formed extracted into an immiscible organic solvent for analysis by gas chromatography [685). 

Sulfide ores usually contain small amounts of mercury, arsenic, selenium, and tellurium, and these impurities volatilize during the ore treatment. All the volatilized impurities, with the exception of mercury, are collected in the dust recovery systems. On account of its being present in low concentrations, mercury is not removed by such a system and passes out with the exit gases. The problem of mercury contamination is particularly pertinent to zinc plants since the sulfidic ores of zinc contain traces of mercury (20-300 ppm). The mercury traces in zinc sulfide concentrates volatilize during roasting and contaminate the sulfuric acid that is made from the sulfur dioxide produced. If the acid is then used to produce phosphatic fertilizers, this may lead to mercury entering the food chain as a contaminant. Several processes have been developed for the removal of mercury, but these are not yet widely adopted. 

Fig. 7B). This behaviour may be attributed to the higher affinity of arsenate for the iron than for aluminium oxides. Table 1. Kinetics of reaction of arsenate (As04) and phosphate (P04) onto Al(OH)x when added alone or as a mixture (As04+ or P04+) (initial As04/P04 molar ratio of 1) at 50% or 100% surface coverage, rf indicates the As04 sorbed/P04 sorbed molar ratio (authors unpublished data, 2007) ... 

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