Feldspar hydroxide

Aluminum [7429-90-5] Al, atomic number 13, atomic weight 26.981, is, at 8.8 wt %, the third most abundant element in the earth s cmst. It is usually found in siUcate minerals such as feldspar [68476-25-5] clays, and mica [12001 -26-2]. Aluminum also occurs in hydroxide, oxide—hydroxide, fluoride, sulfate, or phosphate compounds in a large variety of minerals and ores. 

Formation permeability damage caused by precipitation of dissolved minerals such as colloidal silica, aluminum hydroxide, and aluminum fluoride can reduce the benefits of acidizing (132-134). Careful treatment design, particularly in the concentration and amount of HF used is needed to minimize this problem. Hydrofluoric acid initially reacts with clays and feldspars to form silicon and aluminum fluorides. These species can react with additional clays and feldspars depositing hydrated silica in rock flow channels (106). This usually occurs before the spent acid can be recovered from the formation. However, some workers have concluded that permeability damage due to silica precipitation is much less than previously thought (135). 

Almost all rocks contain some aluminum in the form of aluminum silicate minerals found in clays, feldspars, and micas. Today, bauxite is the major ore for the source of aluminum metal. Bauxite was formed eons ago by the natural chemical reaction of water, which then formed aluminum hydroxides. In addition to the United States, Jamaica and other Caribbean islands are the major sources of bauxite. Bauxite deposits are found in many countries, but not all are of high concentration. 

Goethite is the colored component of yellow ocher a weathering product mainly of siderite, sulfidic ores, and feldspar. It occurs in workable amounts mainly in the Republic of South Africa and France. The Fe2Oa content gives an indication of the iron oxide hydroxide content of the ocher, and is ca. 20% in the French deposits and ca. 55% in the South African. 

Among some kinds of reactions which are slow on a relevant time scale and in particular environments are certain metal-ion oxidations, oxidation of sulfides, sulfate reduction, various metal ion polymerizations (e.g., vanadium, aluminum), aging of hydroxide and oxide precipitates, precipitation of metal-ion silicates and carbonates (e.g., dolomites), conversions among aluminosilicates (e.g., feldspar-kaolinite), and solution or precipitation of quartz (9). Some of these reactions can be accelerated greatly by biological catalysis (e.g., sulfate reduction, metal ion oxidations) (7). 

Arsenic is most prone to form surface complexes by adsorption on metal (mostly iron and manganese) (oxy)(hydr)oxides, followed by clays and feldspars (Lin and Puls, 2003). As discussed in Chapters 3 and 7, iron (oxy)(hydr)oxides are groups of Fe(III) Fe(II) (hydrous) oxides, (hydrous) hydroxides, and (hydrous) oxyhydroxides. Individual compounds, such as ferrihydrite, often have highly variable and... 

Rate-Limiting Steps in Mineral Dissolution 146 Feldspar, Amphibole, and Pyroxene Dissolution Kinetics 148 Parabolic Kinetics 149 Dissolution Mechanism 155 Dissolution Rates of Oxides and Hydroxides 156 Supplementary Reading 161... 

As mentioned earlier, the dissolution of oxides and hydroxides, like feldspars and ferromagnesian minerals, appears to be a surface-controlled reaction. One indication of this is the high E values found by several investigators. Bloom and Erich (1987) obtained E values ranging from 59 4.3 to 67 0.6 kj mol"1 for gibbsite dissolution in acid solutions (pH 1.5-4.0). These values are much higher than for diffusion-controlled reactions reported earlier. 

Aluminum occurs widely in nature in silicates such as micas and feldspars, complexed with sodium and fluorine as cryolite, and in bauxite rock, which is composed of hydrous aluminum oxides, aluminum hydroxides, and impurities such as free silica (Cotton and Wilkinson 1988). Because of its reactivity, aluminum is not found as a free metal in nature (Bodek et al. 1988). Aluminum exhibits only one oxidation state (+3) in its compounds and its behavior in the environment is strongly influenced by its coordination chemistry. Aluminum partitions between solid and liquid phases by reacting and complexing with water molecules and anions such as chloride, fluoride, sulfate, nitrate, phosphate, and negatively charged functional groups on humic materials and clay. 

Fe203, Ti02, MgO, and CaO are nearly always present in kaolinite samples and K20 and Na20 are usually present. Most samples either have excess Si02 or A1203-Mineral impurities such as quartz, anatase, rutile, pyrite, limonite, feldspar, mica, montmorillonite, and various iron and titanium oxides are commonly present in addition to a number of other minerals. Si and Al, in the form of hydroxides, apparently can occur as coatings on the kaolinite layers. Although many of these impurities are usually identified, seldom is the analysis sufficiently quantitative to determine if all the deviation from the ideal composition is due to these impurities. 

During the process of weathering, new kinds of minerals, the secondary minerals, are synthesised. As well as precipitates (hydroxides, oxides, sulphates, carbonates and phosphates) there are the clay minerals. For example, potassium feldspar can hydrolyse and lead to the formation of kaolinite ... 

The largest collector surface for elements impinging on the Globe is the sea, of course. Heavy elements deposited in seawater are enriched in certain sediments such as manganese nodules, iron-manganese hydroxides. Fission tracks were found [83] in feldspar inclusions in such nodules, but no evidence was obtained [40,45] for spontaneous fission activities by counting nodules with neutron detectors. 

Fe-hydroxide, hematite, philipiste, K-feldspar, saponite mixed layer chlorite-smectite, Na zeolite pyrite, saponite prehnite, quartz, sphene... 

Barium oxide is introduced into glass as BaCOs, less frequently as BaSO, or in the case of optical glasses as Ba(N03)2- The most frequently used lead taw materia] is Pb304 (minium, red lead) or PbO, and possibly also the less volatile lead silicate. Small amounts of AI2O3 enter glass as subsidiary components of sand and limestone. If a higher alumina content is required, use is made of aluminium oxide or hydroxide, feldspar, kaolin, phonolite, etc. 

Natural kaolin is treated by washing, in order to remove the coarser particles and impurities such as quartz, feldspars, etc. For some purposes, use is also made of crude kaolin (e.g. in fireclay manufacture). Clays are more widespread in nature they are usually contaminated with larger amounts of quartz, feldspar, mica, etc. Clays containing larger or smaller amounts of aluminium hydroxides (diaspore or gibbsite) occur and are used as ceramic raw materials in some countries. 

Aluminum is the third most abundant element in the earth s crust (after oxygen and silicon), accounting for 8.2% of the total mass. It occurs most commonly in association with silicon in the aluminosilicates of feldspars and micas and in clays, the products of weathering of these rocks. The most important ore for aluminum production is bauxite, a hydrated aluminum oxide that contains 50% to 60% AI2O3 1% to 20% FeiOs 1% to 10% silica minor concentrations of titanium, zirconium, vanadium, and other transition-metal oxides and the balance (20% to 30%) water. Bauxite is purified via the Bayer process, which takes advantage of the fact that the amphoteric oxide alumina is soluble in strong bases but iron(III) oxide is not. Crude bauxite is dissolved in sodium hydroxide... 

Many dissolution reactions, however, are not dependent on adsorbed H or OH , but are first-order with respect to solution concentrations of these ions. Examples of reactions that are first-order with respect to [H ] include feldspar dissolution at pH <2.9 nepheline dissolution in the pH range of 3 to 6 and the dissolution of naturally weathered olivine (Grandstaff, 1986). The results of Grandstaff (1986) for olivine contradict the previously mentioned conclusions of Blum and Lasaga (1989) concerning a first-order dependence on H adsorption sites for freshly crushed olivine. The dissolution of aluminum oxides and hydroxides is first-order with respect to [OH ] at pH >8. 

Figure 3. SEM/EDX images of (a) ferric hydroxide coating on a feldspar grain, (b) EDX spectra of ferric hydroxide on a quartz grain, (c) chemical weathering of biotite platelets, and (d) etch pits on a plagioclase mineral grain. All grains were taken from surface sediments of Lake Cristallina, Switzerland. Photographs are courtesy of Professor Rudolf Giovanoli, Laboratory of Electron Microscopy, University of Bern.

Mineral, upper part B Feldspar Carbonic acid high CO2 partial pressure (Primary/secondary Al-silicate) -1- H2CO3 + H20 (secondary Al-silicate/hydroxide) + (Mg, Ca, Na, K)+ + HCO3 + H4S104 Fast incongruent dissolution... 

Clinoptilolite-H palygorskite-Hcalcite K-feldspar-1-dolomite-1-quartz Clinoptilolite-H sepiolite-Hcalcite K-feldspar-h dolomite-1-quartz Amorphous hydroxides (mainly Fe)- - H4Si04-H Mg " -> Fe-montmorillonite Nontronite -1- Mg + + reduced sulfur->saponite + FeSa Dissolved silica adsorption by clay minerals Amorphous aluminosilicate reconstitution ... 

The glass, opal silica and zeolites are the components of pozzolanas active in the presence of calcium hydroxide. However, pozzolanas contain also a large amount of inert components, to which the crystalline phases, such as quartz, feldspars, dolomite, magnetite, pyroxenes and calcite belong. Pozzolanas can also contain harmful for concrete durability components i.e. organic substances and swelling clays (montmorillonite). 

Synonyms Aluminosilicic acid, sodium salt Aluminum sodium silicate Silicic acid, aluminum sodium salt Sodium aluminosilicate Sodium aluminum silicate Sodium feldspar Zeolite Zeolites Definition Series of hydrated sodium aluminum silicates produced by reaction of sodium silicate and kaolinite clay Formula NajO AI2O3 SiOa with mole ratio = 1 1 13.2 Properties Wh. fine amorphous powd. or beads, odorless and tasteless insol. in water, alcohol, org. soivs. partly sol. in strong acids and alkali hydroxides 80-100 C pH 6.5-10.5 (20% slurry)... 

Aluminum hydroxide Aluminum silicate, Boron carbide Carbon black Carbon fiber, Cellulose, Feldspar Graphite LX-782 Poly/inyl chloride Slllce Silica, amorphous hydrated. Silica, fumed,... 

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