2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures
2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures
2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures
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Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology<br />
M e t h o d s<br />
The experiments of biological-chemical way of regeneration<br />
were realized by the form of charge leaching tests at<br />
the suspension density 5 % at the temperature of 30 °C, under<br />
continuos stirring for the period of 19 days. The qualitative<br />
changes of investigated zinc ferrite during the process of biologico-chemical<br />
way of regeneration were evaluated by:<br />
• RTG diffraction analysis (diffractometer DROn 2,0<br />
Technsabexport, Russian, FeKa radiation),<br />
• particle size distribution (granulometer Helos and Rodos,<br />
Sympatec GmbH Claustahl Zellerfeld),<br />
• BET adsorption method for measuring the adsorption<br />
surface (Micromeritics, Gemini 2360, in nitrogen atmosphere),<br />
• chemical analysis of the content of Zn and Fe in the<br />
leach (atom absorption spectroscopy on the instrument<br />
Spectra AA-30 ,Varian, Australia).<br />
Results<br />
RTG diffraction analysis of amortised sorbents revealed<br />
except of the rest ferrite zinc (Franklinite, ZnFe 2 O 4 ), which<br />
represents probably the nonreacted cores of micropelets, also<br />
the presence of the formed sulphidic, sulphate, oxidic and<br />
carbidic compounds: b-sphalerite (ZnS), wurtzite (ZnS with<br />
addition of Fe), pyrite (FeS 2 ), melanterite (FeSO 4 . 9H2 O),<br />
elemental sulphur (S), magnetite (Fe 3 O 4 ), hematite (a-Fe 2 O 3 )<br />
and cohenite (Fe 3 C).<br />
The bio-leaching of this product leads to the biologicochemical<br />
degradation of amortised layers located on the surface,<br />
which is accompanied by the extraction of Zn and Fe<br />
to the leach. The changes of the concentration of introduced<br />
elements in the leach in dependence on the time of leaching<br />
are shown in Table I.<br />
The concentration of Zn in the leach during the observed<br />
time interval showed the arising trend, while in the Fe concentration<br />
dependence has been appeared the maximum (after<br />
15 days the concentration of the leached ferrite decreased).<br />
As the realized experiments represent the spontaneous<br />
non-regulated process of biologico-chemical oxidation, it is<br />
possible to assume that the decrease of the Fe concentration<br />
Table I<br />
The time dependence of changes of Zn and Fe concentration<br />
in the leach during the biological-chemical regeneration of<br />
amortised sorbents based on zinc ferrite<br />
Time leaching Concentration Concentration<br />
[days] Fe [g dm –3 ] Zn [g dm –3 ]<br />
0 0.37 0.62<br />
3 0.37 1.21<br />
5 1.48 1.56<br />
7 1.50 1.73<br />
10 1.39 <strong>2.</strong>68<br />
14 0.52 <strong>2.</strong>81<br />
17 0.55 <strong>2.</strong>97<br />
19 0.61 3.19<br />
s416<br />
Fig. 1. Comparison of x-ray phase analysis of zinc ferrite sorbent,<br />
A – primary, b – pasivated, C – biologically and chemicaly<br />
regenerised<br />
Legend: w – wurtzite, F – franclinite, S – sphalerite<br />
was caused by the precipitation of the secondary oxididic<br />
compositions of the iron. This assumption has been confirmed<br />
by the RTG diffraction analysis of the leach. After finishing<br />
the biological-chemical leaching of amortised sorbent the<br />
extinction of the most of secondary structures formed by<br />
sorption of sulphate compositions was observed by the RTG<br />
method (Fig. 1.).<br />
The regenerated sample contained the franklinite, addition<br />
of magnetite, metal zinc and the rest of wurtzite, which<br />
during the observed period manifested itself as refractory<br />
mineral and to its destruction the longer period or the change<br />
of electrochemical conditions of leaching should be needed 9 .<br />
Referring to the reality, that the effectivity (the sorption<br />
capacity) of sorbents is directly connected with the sizes<br />
of their surfaces and inversely with the particles sizes, the<br />
changes of these parameter were also studied (Fig. <strong>2.</strong>). The<br />
process of biological-chemical regeneration caused intense<br />
changes in the adsorption surface of sorbents, it has changed<br />
from the value of <strong>2.</strong>8245 m 2 g –1 at amortised sample to the<br />
value of 6.2543 m 2 g –1 at the regenerated sample.<br />
The expressive change was also registered at the distribution<br />
of the particles sizes. The value of mean particle<br />
diameter has decreased from the value of 9 mm at amortised<br />
sorbent to <strong>2.</strong>19 mm at the regenerated sorbents (Table II).