Neutral lattice minerals

Gibbsite and the "neutral lattice" minerals, 1 1 or 2 1 represent the extremes of chemical variat.on in the clay minerals. Gibbsite is a hydrated form of alumina. Kaolinite and pyrophyllite can be considered to be strictly aluminum-silicates, i.e., no ions other than Al, Si, 0, H are present in appreciable quantities in these minerals. This is not as... 

For various reasons, gibbsite and kaolinite are really the only minerals of the "neutral lattice" type which occur with any frequency in non-metamorphic rocks. These minerals are formed in soils, most noticeably from granitic rocks but are also commonly found forming from basic rocks during the weathering process (Millot, 1964 Tardy, 1969). The... 

Amphiboles. The crystalline stmcture common to amphibole minerals consists of two ribbons of siUcate tetrahedra placed back to back as shown in Figure 5. The plane of anionic valency sites created by this double ribbon arrangement is neutralized by the metal cations. The unit cell has seven cationic sites of three different types these sites can host a large variety of metal cations without substantial dismption of the lattice. 

Smectite is the first secondary mineral to form upon rock weathering in the semi-arid to sub-humid tropics. Smectite clay retains most of the ions, notably Ca2+ and Mg2+, released from weathering primary silicates. Iron, present as Fe2+ in primary minerals, is preserved in the smectite crystal lattice as Fe3+. The smectites become unstable as weathering proceeds and basic cations and silica are removed by leaching. Fe3+-compounds however remain in the soil, lending it a reddish color aluminum is retained in kaolinite and A1-oxides. Leached soil components accumulate at poorly drained, lower terrain positions where they precipitate and form new smectitic clays that remain stable as long as the pH is above neutral. Additional circumstances for the dominance of clays are ... 

Zeolite is a crystalline, porous aluminosilicate mineral with a unique interconnecting lattice structure. This lattice structure is arranged to form a honeycomb framework of consistent diameter interconnecting channels and pores. Negatively charged alumina and neutrally charged silica tetrahedral building blocks are stacked to produce the open three-dimensional honeycomb framework. 

In montmorillonite, similar to other minerals, when the size of the exchanged cation is similar to the pore sizes in the crystal lattice, cations can build into the crystal lattice and, consequently, they reduce the negative layer charge (Chapter 1, Section 1.3.3.2). Other neutral molecules or cationic substances (Chapter 1, Sections 1.3.3.1 and 1.3.3.2) can also be sorbed in the interlayer space and on the external surfaces as well. They play an important role in defining the internal and total surface area and catalytic properties, and they may have an effect on the hydrophobicity of the mineral, as well as playing an important role in the production of pillared materials, etc. 

The other example of the ion sorption on edge sites is the sorption of palladium ions (Nagy and Konya 2007) on montmorillonite. As known, palladium ions are hydrolyzed at such a low pH value where the lattice of clay minerals is destroyed. For this reason, during the preparation of palladium-montmorillonite, we have to avoid the hydrolysis of Pd(II) and the acidic destruction of the clay at the same time. We can do so by applying Pd(II) as positively charged complexes at neutral pH. For example, [Pd(NH3)2]2+ complexes can be prepared from metallic palladium as follows ... 

The ideal constitution of the kaolin layer represents an electrically neutral unit, with rarely any isomorphous substitution of cations of different charges within the lattice. Consequently, kaolinite and related minerals would not be expected to show a large cation exchange capacity, and indeed this is usually the case. That a small but varying exchange capacity does occur may be attributed to two principal causes. 

Some aluminosilicate minerals appear to meet the above criteria rather well, especially with regard to low leachability and chemical and physical stability 1, 2). A low-temperature process for converting the wastes to aluminosilicates with low leachability has now been found (3). Aqueous waste solutions containing NaOH, NaNOa, NaN02, NaAl02, mixed fission products, and minor amounts of other salts are mixed with powdered clays (kaolin, bentonite, halloysite, or dickite) and allowed to react at 30°-100°C to form small crystals of the mineral cancrinite. The sodium aluminosilicate crystal lattice of cancrinite contains large amounts of trapped salts and radioactive fission products. The process is applicable to caustic radioactive liquids such as neutralized Purex wastes or to salts or oxides produced by evaporation or calcination of these liquid wastes. 

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