Phosphate replacement deposits

Although urine remained the only source of the element for nearly 100 years after its discovery, it had been replaced by bones by the end of the eighteenth century. Supplies of the latter soon proved to be inadequate, but fortunately substantial phosphate mineral deposits were quickly found. This enabled serious commercial production of phosphorus compounds from these ores to commence in Europe about 1850, when wet process phosphoric acid became available. In 1888, a major development took place when Readman invented the electric furnace method for the continuous production of the element directly from phosphate ores. In 1890, the first industrial electric furnace came into use at Oldbury in England, and this was followed by similar production at Niagara Falls, USA. 

In the geochemistry of fluorine, the close match in the ionic radii of fluoride (0.136 nm), hydroxide (0.140 nm), and oxide ion (0.140 nm) allows a sequential replacement of oxygen by fluorine in a wide variety of minerals. This accounts for the wide dissemination of the element in nature. The ready formation of volatile silicon tetrafluoride, the pyrohydrolysis of fluorides to hydrogen fluoride, and the low solubility of calcium fluoride and of calcium fluorophosphates, have provided a geochemical cycle in which fluorine may be stripped from solution by limestone and by apatite to form the deposits of fluorspar and of phosphate rock (fluoroapatite [1306-01 -0]) approximately CaF2 3Ca2(P0 2 which ate the world s main resources of fluorine (1). 

Fluorine for industrial use is almost exclusively obtained from fluorite. There are many possible fluorite-ore types. It occurs as fissure-fill and manto-replaced types, and in pegmatites, residual/eluvial deposits, carbonates and phosphate deposits. It is a gangue mineral in many base metal deposits, but due to stringent trace metal requirements often can t be economically beneficiated to a saleable product. Most fluorite ores are selectively mined, and ore from some minor vein deposits is then upgraded to a saleable product by sorting. 

The first two components are the active surfactants, whereas the other components are added for a variety of reasons. The polyphosphate chelate Ca ions which are present (with Mg ions also) in so-called hard waters and prevents them from coagulating the anionic surfactants. Zeolite powders are often used to replace phosphate because of their nutrient properties in river systems. Sodium silicate is added as a corrosion inhibitor for washing machines and also increases the pH. The pH is maintained at about 10 by the sodium carbonate. At lower pH values the acid form of the surfactants are produced and in most cases these are either insoluble or much less soluble than the sodium salt. Sodium sulphate is added to prevent caking and ensures free-flowing powder. The cellulose acts as a protective hydrophilic sheath around dispersed dirt particles and prevents re-deposition on the fabric. Foam stabilizers (non-ionic surfactants) are sometimes added to give a... 

As discussed in Chapters 5 and 7, the use of lime to precipitate calcium arsenates is a common method for removing inorganic As(V) from water or flue gases. Calcium arsenates were also once extensively used in pesticides (Chapter 5). The compositions of some calcium arsenates, such as johnbaumite (Ca5(As04)3(0H) Table 2.5), resemble the very common phosphate mineral, apatite (Ca5(P04)3(F,Cl,0H)), where arsenate replaces phosphate. Some lead arsenates, such as mimetite (Pb5(As04)3Cl Table 2.5), also have crystalline structures that are related to apatite. Mimetite may occur in oxidized lead-rich hydrothermal deposits. 

The phosphates of lime which occur in nature or are produced during the course of manufacture of phosphorus compounds are salts of orthophosphoric acid. The hydrogen is replaced by calcium in stages giving successively mono-, di- and tri-calcium phosphate. Of these the mono-calcium salt alone is freely soluble. The solids deposited on evaporation, or obtained by double decomposition, are generally mixtures of the di-, tri- or more basic compounds, but pure crystalline forms have been prepared, especially of the more acid phosphates. The more basic phosphates are very sparingly soluble, and the solubilities are not definite. The solids are not in equilibrium with solutions of their own composition, but are in process of transformation which is so slow that equilibrium is not attained in most operations. 

Vitamin D hormone is derived from vitamin D (cholecalciferol). Vitamin D can also be produced in the body it is formed in the skin from dehydrocholesterol during irradiation with UV light. When there is lack of solar radiation, dietary intake becomes essential, cod liver oil being a rich source. Metabolically active vitamin D hormone results from two successive hydroxylations in the liver at position 25 (- calcifediol) and in the kidney at position 1 (- calcitriol = vitamin D hormone). 1-Hydroxylation depends on the level of calcium homeostasis and is stimulated by parathormone and a fall in plasma levels of Ca2+ and phosphate. Vitamin D hormone promotes enteral absorption and renal reabsorption of Ca2+ and phosphate. As a result of the increased Ca2+ and phosphate concentration in blood, there is an increased tendency for these ions to be deposited in bone in the form of hydroxyapatite crystals. In vitamin D deficiency, bone mineralization is inadequate (rickets, osteomalacia). Therapeutic use aims at replacement. Mostly, vitamin D is given in liver disease, calcifediol may be indi-... 

Phosphorite, for our purposes, is the term applied to calcium phosphate rocks, whether they are accumulations of bones, precipitates directly from sea water or replacements of calcareous rocks. They are very extensive on the earth, occurring on all continental land masses with the possible exception of Antarctica, where commercial deposits have not yet been found. Phosphorites comprise the principal geologic storage bin for inorganic phosphates. 

The above-mentioned organic acids may be expected to produce conditions in which silica of silicate minerals is dissolved, and — assuming the phosphate concentration is adequate or sufficient time has elapsed at lower concentrations — the silicate minerals become replaced by phosphate minerals. Although little is known concerning the conditions of oxidation vs. reduction encountered in guano deposits, such a mode of replacement must be attributed to the conversion of feldspar laths to variscite-metavariscite at Malpelo Island (McConnell, 1943). Indeed, the conditions may be aerobic at the surface, whereas anaerobic conditions obtain at the lower portions in contact with the country rock. 

The tissue engineering concept offers development of useful substrates for repair replacement or regeneration of organs and tissues. Hydroxyapatite (Cio(PC>4)6(OH)2, HA) is the major constituent of the bone and teeth. Deposition of calcium phosphate... 

Implants for bone replacement applications — Grafting of phosphate methacrylate esters onto fluoro polymers to enhance caicium deposition. 

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