Biochemical nature of gley formation during aging of clayey materials (Review)

Abstract

The biochemical nature of gley formation during aging of clayey materials (CMs), the factors under which the process arises, methods of identification, and its effect on the properties of CMs are examined. It is shown that necessary factors are the moisture content of CMs and the content of organic matter and natural microflora as well as maintaining the optimal temperature during the aging period. A comprehensive assessment using color characteristics, the redox state of the medium, and chemical criteria based on the ratio of the forms of iron compounds, is proposed for identifying the biochemical processes and determining the optimal aging time of CMs.

Fe(III) Bioreduction in a Kaolin Suspension in Storage

“…The combined redox potential [7], which takes account of the protons (pH) and the electrons ( pe), viz., rH = 2 ( pe + pH), was used to determine the redox state of the kaolin suspension.…”

“…But, unfortunately, the need to maintain the purity of the cultures of the microorganisms introduced complicates the technological process of removing iron [1]. Since iron-reducing microorganisms are common in the environment [6], the most practical variant is to use naturally occurring microorganisms separated beforehand from natural sources, which have already adapted to local conditions [7,8]. To support the development of natural types of microorganisms participating in iron reduction there is no need to sterilize the initial raw material (sterilization is an expensive process and unrealistic under production conditions).…”

Nature of the liquefaction and fluidity of kaolin from the Zhuravlinyi Log deposit (Review)

“…However, in moistened kaolin, the functioning of the biota accelerates the process of particle disaggregation and peptization of clayey minerals due to the action of the metabolites, some of which -the organic acids -act as surfactants while others -mineral and organic acids -dissolve inorganic amorphous compounds and weakly crystallized minerals cementing the particles [9,27]. The multiplicity of abiotic and biochemical processes occurring can be reduced to three main effects on kaolin: disaggregation of particles and dispersing of the minerals to dissolution, migration of Si, Al, and Fe in the form of a suspension and their reprecipitation on the walls of pores and on the surface of aggregates.…”

“…Selective dissolution is used mainly to identify and perform quantitative determination of the amorphous inorganic compounds (aluminosilicate gels and iron oxides) and poorly crystallized clayey minerals. The most commonly used method is Tamm extraction (pH = 3.3) [9,27,30]. As the elements Si, Al, and Fe migrate into the Tamm solution the values for ZLD kaolin (over 29 samples) 0.20 -5.90, 0.10 -2.30, and 0.30 -1.60 mg/liter, respectively, exceed the values for Prosyanovskoe kaolin and Latnenskoe and Chasov-Yar clays but are much lower than the values for Troshkovskoe clay (54.5, 20.5, and 3.50 mg/liter).…”

“…It is shown in [15] that the EPR signals in a weak magnetic field g~4.0, which were recorded in the form of a triplet, are ordinarily interpreted as a superposition of the spectra of two centers: Fe(I) centercentral line with g~4. 27 and Fe(II) center with side lines with g values 4.9, 3.7, and 3.5. There is no single opinion concerning the structural position of Fe 3+ ions.…”