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 />
P38 bIOLOGICAL-ChEMICAL REGENERATION<br />
OF DESuLPhuRIZATION SORbENTS bASED<br />
ON ZINC FERRITE<br />
MáRIA KUŠnIEROVá, ALEnA LUPTáKOVá,<br />
VLADIMíR ŠEPELáK and MáRIA PRAŠČáKOVá<br />
Institute of Geotechnics SAS, Watsonova 45, 043 53 Kosice,<br />
Slovak Republic,<br />
kusnier@saske.sk<br />
Introduction<br />
The energetic demands of people in present, as well<br />
as in the future will be supplied mainly by the energy from<br />
the fossil sources, which is accompanying with the negative<br />
impact on the environment in the form of emissions of sulphate<br />
and carbonate compounds. For desulphurization and<br />
decarbonization of these emissions more commercial technological<br />
methods have been developed, to which belongs<br />
also the utilization of solid sorbents (filters) based on the zinc<br />
ferrite. The studies of Grindly 1 and Krisham 2 helped to clear<br />
up the high-temperature process of desulphurization of waste<br />
gases after coal combustion which can be described by the<br />
chemical equation:<br />
3ZnFe 2 O 4 + 3 H 2 S + H 2 → ZnS + 2FeS + 4H 2 O (1)<br />
In dependence on the conditions of the combustion process<br />
there is according to the Lamoreaux 3 a possibility of a<br />
occurring of another reaction of the iron (occurring in the<br />
solid sorbents) with waste gases of carbon, leading to formation<br />
of carbide. This is governed by the equations:<br />
3FeO + CO → Fe 3 C + 2O 2<br />
3Fe + CO → Fe 3 C + ½O 2<br />
The phase composition of sulphurized (amortised) sorbents<br />
shows the presence of sulphidic and carbidic structures<br />
located mainly on the surface of particles of zinc ferrite<br />
(respectively Zn Fe 2 O 3 – micropellets of zinc ferrite). They<br />
became inactive and the further utilization is constrained to<br />
their regeneration. In relation with the most effective methods<br />
of manifold recycling of sorbents, several methods of their<br />
regeneration were studied.<br />
The literature shows two methods of regeneration of<br />
sulphatizing sorbents based on zinc ferrite. The first method<br />
commercially used, is a oxidising pyrolysis of sulphides 2 . In<br />
this process are the sulphidic structures in dependence on the<br />
temperature of the oxidising rousting transformed step by<br />
step at the first stage to the sulphates and at the second stage<br />
which corresponds to the temperature of sulphates decomposition<br />
(in the temperature range from 480 to 600 °C) to the<br />
oxides, according to the equations (4) and (5):<br />
2FeS + 3.5O 2 → Fe 2 O 3 + 2SO 2<br />
(2)<br />
(3)<br />
(4)<br />
s415<br />
ZnS + 1.5O 2 → ZnO + SO 2<br />
The second method of the regeneration of desulphurization<br />
sorbents which is introduced by Sakao 4 , is based on the<br />
principle of pressure leaching of ZnS in water environment at<br />
the temperature over 550 °C. This method is described by the<br />
equation, almost identical with the Eq. (5):<br />
ZnS + 1.5O 2 → ZnO + SO 2<br />
The commercially available technologies of sulphides<br />
processing and treatment (as sources of colour and rare<br />
metals) have nowadays started with utilization of biologicalchemical<br />
processes (bio-leaching); where the physical and<br />
chemical base of degradation of sulphidic structures is identical<br />
with the methods of regeneration of desulphurization<br />
sorbents mentioned above.<br />
The principle of all mentioned methods is the process of<br />
sulphides oxidation with utilization of various methods of catalysis.<br />
In the process of thermic regeneration is the oxidising<br />
reaction catalysed by the thermic energy, at pressure leaching<br />
by the pressure and temperature.<br />
The aim of this paper is to testify the biological-chemical<br />
method as a new method of sorbents regeneration, utilising<br />
the catalytic effect of the metabolism of an acidophilous bacteria<br />
– Thiobacillus ferrooxidans, oxidising the sulphate and<br />
iron 8 .<br />
Experimental<br />
M a t e r i a l<br />
Zinc ferrite<br />
For biological-chemical regeneration, zinc ferrite after<br />
sulphurization test was used.The powder sample containing<br />
90 % zinc ferrite and 10 % bentonite binder by weight was<br />
pelletized to cylindrical pellets, calcined in air from room<br />
temperature to 970 K, and crushed and sieved to the size<br />
of a stainless steel cylinder, in which 25 g of pelletized sorbent<br />
was packed.The simulated coal gas had the following<br />
composition: 30 % vol. CO, 50 % vol. n 2 , 19.5 % vol. H 2 ,<br />
and 0.5 % vol. H 2 S. Total gas flow-rate diring absoption was<br />
5,000 cm 3 min –1 . The desulphurization tests were stopped<br />
when the H 2 S concentration of the effluent gas was above<br />
50 ppm. The details of the sulphurization experiments are<br />
described also in our previous papers 6,7 .<br />
bacteria<br />
The bacteria used in experiments was: Thiobacillus<br />
ferrooxidans, isolated from the mining drainage waters of<br />
sulphides deposits, which is cultivated for a long time on<br />
the sphalerite (ZnS) substrates. The leaching solution was<br />
formed by cultivated medium according to the Silverman<br />
and Lundgren 5 , in which the cells of bacteria were scattered.<br />
The pH value of the solution at the beginning of the reaction<br />
was 1.6.<br />
(5)<br />
(6)