2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P38 bIOLOGICAL-ChEMICAL REGENERATION
OF DESuLPhuRIZATION SORbENTS bASED
ON ZINC FERRITE
MáRIA KUŠnIEROVá, ALEnA LUPTáKOVá,
VLADIMíR ŠEPELáK and MáRIA PRAŠČáKOVá
Institute of Geotechnics SAS, Watsonova 45, 043 53 Kosice,
Slovak Republic,
kusnier@saske.sk
Introduction
The energetic demands of people in present, as well
as in the future will be supplied mainly by the energy from
the fossil sources, which is accompanying with the negative
impact on the environment in the form of emissions of sulphate
and carbonate compounds. For desulphurization and
decarbonization of these emissions more commercial technological
methods have been developed, to which belongs
also the utilization of solid sorbents (filters) based on the zinc
ferrite. The studies of Grindly 1 and Krisham 2 helped to clear
up the high-temperature process of desulphurization of waste
gases after coal combustion which can be described by the
chemical equation:
3ZnFe 2 O 4 + 3 H 2 S + H 2 → ZnS + 2FeS + 4H 2 O (1)
In dependence on the conditions of the combustion process
there is according to the Lamoreaux 3 a possibility of a
occurring of another reaction of the iron (occurring in the
solid sorbents) with waste gases of carbon, leading to formation
of carbide. This is governed by the equations:
3FeO + CO → Fe 3 C + 2O 2
3Fe + CO → Fe 3 C + ½O 2
The phase composition of sulphurized (amortised) sorbents
shows the presence of sulphidic and carbidic structures
located mainly on the surface of particles of zinc ferrite
(respectively Zn Fe 2 O 3 – micropellets of zinc ferrite). They
became inactive and the further utilization is constrained to
their regeneration. In relation with the most effective methods
of manifold recycling of sorbents, several methods of their
regeneration were studied.
The literature shows two methods of regeneration of
sulphatizing sorbents based on zinc ferrite. The first method
commercially used, is a oxidising pyrolysis of sulphides 2 . In
this process are the sulphidic structures in dependence on the
temperature of the oxidising rousting transformed step by
step at the first stage to the sulphates and at the second stage
which corresponds to the temperature of sulphates decomposition
(in the temperature range from 480 to 600 °C) to the
oxides, according to the equations (4) and (5):
2FeS + 3.5O 2 → Fe 2 O 3 + 2SO 2
(2)
(3)
(4)
s415
ZnS + 1.5O 2 → ZnO + SO 2
The second method of the regeneration of desulphurization
sorbents which is introduced by Sakao 4 , is based on the
principle of pressure leaching of ZnS in water environment at
the temperature over 550 °C. This method is described by the
equation, almost identical with the Eq. (5):
ZnS + 1.5O 2 → ZnO + SO 2
The commercially available technologies of sulphides
processing and treatment (as sources of colour and rare
metals) have nowadays started with utilization of biologicalchemical
processes (bio-leaching); where the physical and
chemical base of degradation of sulphidic structures is identical
with the methods of regeneration of desulphurization
sorbents mentioned above.
The principle of all mentioned methods is the process of
sulphides oxidation with utilization of various methods of catalysis.
In the process of thermic regeneration is the oxidising
reaction catalysed by the thermic energy, at pressure leaching
by the pressure and temperature.
The aim of this paper is to testify the biological-chemical
method as a new method of sorbents regeneration, utilising
the catalytic effect of the metabolism of an acidophilous bacteria
– Thiobacillus ferrooxidans, oxidising the sulphate and
iron 8 .
Experimental
M a t e r i a l
Zinc ferrite
For biological-chemical regeneration, zinc ferrite after
sulphurization test was used.The powder sample containing
90 % zinc ferrite and 10 % bentonite binder by weight was
pelletized to cylindrical pellets, calcined in air from room
temperature to 970 K, and crushed and sieved to the size
of a stainless steel cylinder, in which 25 g of pelletized sorbent
was packed.The simulated coal gas had the following
composition: 30 % vol. CO, 50 % vol. n 2 , 19.5 % vol. H 2 ,
and 0.5 % vol. H 2 S. Total gas flow-rate diring absoption was
5,000 cm 3 min –1 . The desulphurization tests were stopped
when the H 2 S concentration of the effluent gas was above
50 ppm. The details of the sulphurization experiments are
described also in our previous papers 6,7 .
bacteria
The bacteria used in experiments was: Thiobacillus
ferrooxidans, isolated from the mining drainage waters of
sulphides deposits, which is cultivated for a long time on
the sphalerite (ZnS) substrates. The leaching solution was
formed by cultivated medium according to the Silverman
and Lundgren 5 , in which the cells of bacteria were scattered.
The pH value of the solution at the beginning of the reaction
was 1.6.
(5)
(6)