2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
M e t h o d s
The experiments of biological-chemical way of regeneration
were realized by the form of charge leaching tests at
the suspension density 5 % at the temperature of 30 °C, under
continuos stirring for the period of 19 days. The qualitative
changes of investigated zinc ferrite during the process of biologico-chemical
way of regeneration were evaluated by:
• RTG diffraction analysis (diffractometer DROn 2,0
Technsabexport, Russian, FeKa radiation),
• particle size distribution (granulometer Helos and Rodos,
Sympatec GmbH Claustahl Zellerfeld),
• BET adsorption method for measuring the adsorption
surface (Micromeritics, Gemini 2360, in nitrogen atmosphere),
• chemical analysis of the content of Zn and Fe in the
leach (atom absorption spectroscopy on the instrument
Spectra AA-30 ,Varian, Australia).
Results
RTG diffraction analysis of amortised sorbents revealed
except of the rest ferrite zinc (Franklinite, ZnFe 2 O 4 ), which
represents probably the nonreacted cores of micropelets, also
the presence of the formed sulphidic, sulphate, oxidic and
carbidic compounds: b-sphalerite (ZnS), wurtzite (ZnS with
addition of Fe), pyrite (FeS 2 ), melanterite (FeSO 4 . 9H2 O),
elemental sulphur (S), magnetite (Fe 3 O 4 ), hematite (a-Fe 2 O 3 )
and cohenite (Fe 3 C).
The bio-leaching of this product leads to the biologicochemical
degradation of amortised layers located on the surface,
which is accompanied by the extraction of Zn and Fe
to the leach. The changes of the concentration of introduced
elements in the leach in dependence on the time of leaching
are shown in Table I.
The concentration of Zn in the leach during the observed
time interval showed the arising trend, while in the Fe concentration
dependence has been appeared the maximum (after
15 days the concentration of the leached ferrite decreased).
As the realized experiments represent the spontaneous
non-regulated process of biologico-chemical oxidation, it is
possible to assume that the decrease of the Fe concentration
Table I
The time dependence of changes of Zn and Fe concentration
in the leach during the biological-chemical regeneration of
amortised sorbents based on zinc ferrite
Time leaching Concentration Concentration
[days] Fe [g dm –3 ] Zn [g dm –3 ]
0 0.37 0.62
3 0.37 1.21
5 1.48 1.56
7 1.50 1.73
10 1.39 2.68
14 0.52 2.81
17 0.55 2.97
19 0.61 3.19
s416
Fig. 1. Comparison of x-ray phase analysis of zinc ferrite sorbent,
A – primary, b – pasivated, C – biologically and chemicaly
regenerised
Legend: w – wurtzite, F – franclinite, S – sphalerite
was caused by the precipitation of the secondary oxididic
compositions of the iron. This assumption has been confirmed
by the RTG diffraction analysis of the leach. After finishing
the biological-chemical leaching of amortised sorbent the
extinction of the most of secondary structures formed by
sorption of sulphate compositions was observed by the RTG
method (Fig. 1.).
The regenerated sample contained the franklinite, addition
of magnetite, metal zinc and the rest of wurtzite, which
during the observed period manifested itself as refractory
mineral and to its destruction the longer period or the change
of electrochemical conditions of leaching should be needed 9 .
Referring to the reality, that the effectivity (the sorption
capacity) of sorbents is directly connected with the sizes
of their surfaces and inversely with the particles sizes, the
changes of these parameter were also studied (Fig. 2.). The
process of biological-chemical regeneration caused intense
changes in the adsorption surface of sorbents, it has changed
from the value of 2.8245 m 2 g –1 at amortised sample to the
value of 6.2543 m 2 g –1 at the regenerated sample.
The expressive change was also registered at the distribution
of the particles sizes. The value of mean particle
diameter has decreased from the value of 9 mm at amortised
sorbent to 2.19 mm at the regenerated sorbents (Table II).