PURIFICATION OF KAOLIN OF DIFFERENT GRADES WITH APPLICATION OF SILICATE MICROORGANISMS - Biochemistry and Biotechnology: Research and Development - page 165

It is necessary to note considerable decrease (almost in 2 times), on account of denial of
application of expensive washing by diluted hydrochloric acid, volumes of discharge and
washing solutions on all stages of processing.
Different microorganisms participate in degradation of main types of aluminum silicate
minerals. These microorganisms are capable on account of synthesis of extracellular organic
acids to transfer into soluble state compositions of calcium, potassium, titanium, silicon
present in form of admixtures, which promotes to kaolin purification.
Destruction of silicate minerals is indirect process based on action of exometabolites
produced by microorganisms in specific conditions of medium. To receive the maximum
yield of acids it is necessary to strictly observe specific composition of medium and
cultivation conditions. Production of organic acids by fungi demands on intensive aeration. It
is reached by cultivation of micromycetes by surface method in vessels with thin layer of
nutrient medium or by submerged method but in special bioreactors where aeration is
conducted by mechanical stirring and insufflations of sterile air under pressure.
Selectivity and specificity of microbial destruction of silicate minerals is observed. This
process depends on physiological peculiarities of microorganisms and formed by them
organic and mineral acids, exopolysaccharides and other surface-active substances, and on
type of silicate minerals and their crystal-chemical peculiarities as well.
Screening conducted among microorganisms on ability to synthesize organic acids
allowed to select a number of microorganisms (Bacillus subtitlis var.mucilaginosus, Bacillus
subtilis, Thrichodеrma harzianum, Aspergillus niger). Di-, tri- and polycarboxilic acids,
aminoacids, were determined in cultural broth of these microorganisms; and galactose and
glucose was determined among exopolysaccharides. Maximum content of organic acids with
prevailing content of citric acid was observed in cultural broth of Bacillus sp. (9.2 U),
Aspergillus niger (13.4 U) and Thrichodеrma harzianum (18.3 U).
We conducted model tests on kaolin bioleaching of AKS grade with application of
selected microorganisms by single-stage scheme.
Preliminary cultivation of bacteria was conducted on experimental nutrient medium with
addition of plant wastes. It is known that plant wastes are good substrate for cultivation of
micromycetes. It results in production of organic acids, partial saccharification of substrate,
production of polysaccharides, which presence promotes to improvement of plasticity of
clays.
Kaolin of AKS grade was treated by filtrated solution of cultural broth at content solid:
liquid =1:5, with presence of organic acids up to 25 U during 2 days.
Organic acids produced by these microorganisms in process of purification form complex
links with elements incorporated in composition of crystal lattice of minerals, and thus,
promote to minerals' dispersion. Obtained date testify that at treatment by cultural broth
Fe 2 O 3 content in kaolin decreases almost in 3 times and reaches 0.23% (table 2).
Received results reveal that treatment by bacterial solutions considerably improves
quality of kaolin of AKS grade and increases level of its whiteness.
Thus, experimental results testify possibility of application of both thionic iron-oxidizing
and microorganisms synthesizing organic acids for biopurification of kaolin of different
grades.