Gibbsite crystalline

McBride, M.C. (1985) Influence of glycine on Cu adsorption by micro crystalline gibbsite and goethite. Clays Clay Min. 33 397-402 McCafferty, E. Zettlemoyer, A.C. (1970) Entropy of adsorption and the mobility of water vapor on a- Fe20. J. Colloid Interface Sci. 34 452-460... 

Once a solid mineral phase is introduced into this simple model and cation exchange or dissolution/precipitation reactions are allowed for, the relationships among pH, and added acidity or basicity are fundamentally changed. For example, the H" ions can react with the acid mineral soil to produce soluble AF. Figure 5.6 showed that the solubility of AF in the B and C horizons of some acid mineral soils is described fairly well by the solubility product of crystalline gibbsite ( so = [AF ][0H ] = 10 ), so that the approximate relationship between [AF ] and [H ] is... 

As a corollary to constant AP, it should be noted that AP + AP concentration stays constant with aging time. Equilibrium is reached in the systems when the AP and AP + AP lines reach the dotted line indicating the amount of crystalline gibbsite that should be present at equilibrium as a function of pH. After a few days aging, the equilibrium pH for a system can be accurately predicted by extrapolating the AP + AP curve, which appears to be usually a straight line parallel to the pH axis, to its intersection with the dotted gibbsite concentration curve. 

The starting material for processing porous alumina is crystalline gibbsite, A1(0H)3, which is subjected to a heat treatment, under controlled conditions, between 500 and 800° C. During this process, water is released, leaving crystalline porous alumina (y-alumina) (Unger, 1990). 

The sample RO showed also the presence of poorly crystalline gibbsite the Rl-RlO samples showed the presence of (aluminous) ferrihydrite. 

Figure 13. Temperature dependence of the transformation degree of ( , , 0)-Al(OH)3 obtained by deintercalation lithium chloride from well crystalline LADH-Cl - fine well crystalline gibbsite.Q- 303K - 308K D, - 313K. [LiCl]-190g/l.

A predominance diagram relevant to zero ionic strength is illustrated in Figure 13.16, where the assumed solid phase is crystalline gibbsite, Al(OH)3(s). 

The term alumina hydrates or hydrated aluminas is used in industry and commerce to designate aluminum hydroxides. These compounds are tme hydroxides and do not contain water of hydration. Several forms are known a general classification is shown in Figure 1. The most weU-defined crystalline forms ate the trihydroxides, Al(OH) gibbsite [14762-49-3], bayerite [20257-20-9], and nordstrandite [13840-05-6], In addition, two aluminum oxide—hydroxides, AIO(OH), boelimite [1318-23-6] and diaspote [14457-84-2], have been clearly defined. The existence of several other forms of aluminum hydroxides have been claimed. However, there is controversy as to whether they ate truly new phases or stmctures having distorted lattices containing adsorbed or intedameUar water and impurities. 

Commercial production of bayerite is relatively small and employs CO2 neutralization of caustic aluminate Hquor obtained from either Bayer or sinter processes. The product obtained is about 90% crystalline bayerite having small amounts of gibbsite, pseudoboehmite, and amorphous aluminum hydroxides. 

The solid phase resulting from this reaction typically forms a white precipitate, which on account of its low density often forms impressive masses of white foam where the water, from which it is precipitating, is subjected to turbulent eddies. Generally, this white precipitate is X-ray amorphous, although if it is allowed to settle for periods in excess of six months, crystalline forms of Al(OH)3, most notably gibbsite, are... 

Iron(III) oxide or alumina is refined from bauxite. Approximately 175 million tons of bauxite are mined annually worldwide, with virtually all of this processed into alumina. Alumina is a white crystalline substance that resembles salt. Approximately 90% of all alumina is used for making aluminum, with the remainder used for abrasives and ceramics. Alumina is produced from bauxite using the Bayer process patented in 1887 by Austrian Karl Josef Bayer (1847-1904). The Bayer process begins by grinding the bauxite and mixing it with sodium hydroxide in a digester. The sodium hydroxide dissolves aluminum oxide components to produce aluminum hydroxide compounds. For gibbsite, the reaction is Al(OH)3 + NaOH —> Al(OH)4 + Na+. Insoluble impurities such as silicates, titanium oxides, and iron oxides are removed from the solution while sodium hydroxide is recovered and recycled. Reaction conditions are then... 

However, before considering such a complex system of four independent variables, which is represented in planar perspective, let us first take the variables as they can be represented in a sequence of change from inert components which, one by one, become "perfectly mobile" or intensive variables of a thermodynamic system. We will first assume that the phases which will be present in some portion of the system are gibbsite, kaolinite, crystalline or amorphous silica, mica, illite, mixed layered illite-montmorillonite (beidellite), K-feldspar (no pure potassium zeolite is present). Initially we will simplify the mineralogy in the following way ... 

G = gibbsite, Kaol = kaolinite, Q = amorphous or crystalline SiO, Mi = potassic mica, Mo = K-beidellite, ML = mixed layered mica-montmorillonite minerals, F = potassium feldspar, Py = pyrophyllite. This is necessary to simplify portions of the diagrams where our knowledge of phase relations is not sufficient to judge the roles which each individual mineral will play. 

It was easier to prepare clays using cations that formed a brucite structure rather than those forming a gibbsite structure. This is, in part, due to the difficulty of forming octahedrally coordinated Al3+ compounds in the presence of silicon at other than low pH conditions. Henin and co-workers believed that hydroxide sheets are formed on which silica is subsequently fixed. The presence of silica tends to cause the hydroxides to precipitate at lower pH than they normally do. Most of these experiments were carried on at 100°C, although crystalline products were obtained at temperatures of 20°C. The rate of formation varies in the ratio 1 560 between 0°C and 100°C. 

The application of the GLO Step Rule and, for that matter, the interpretation of activity-ratio diagrams in general are influenced by the existence of varying degrees of crystallinity or of particle size in soil minerals, with a corresponding variation in their solubility.15 For example, in the case of Fig. 3.5, very poorly crystallized forms of gibbsite and kaolinite, alluded to above, would require... 

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