2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P95 MICROwAVE DESuLPhuRIZATION OF COAL
InGRID ZnAMEnáČKOVá, MICHAL LOVáS, SILVIA
ČUVAnOVá and ŠTEFAn JAKABSKý
Institute of Geotechnics, SAS, Watsonova 45, 043 53 Košice,
Slovakia,
znamenackova@saske.sk
Introduction
Microwave heating has been used in several studies of
the coal desulfurization. Desulphurization by microwaves is
closely related to the form of sulphur compound in the coal,
the physical and chemical structure, as well as the chemical
activity of the leachant. The ability of molten naOH to desulfurize
the coal has been known for more than three decades.
The process known as molten caustic leaching (MCL) was
tested for the first time in the USA. The objective was the
removing of the mineral components, pyritic and organic sulfur
by the reaction of coal with a mixture of molten sodium
and potassium hydroxides. The MCL process was effectively
applied for the treatment of the Slovak brown coal 1 . Balaz
et al. reported the use of simultaneous grinding and alkaline
chemical leaching process (GACL) on brown coal and found
that more than 41 % of total sulphur reduction was achieved.
Magnetic methods of mineral removal from coal depend
on the difference in the magnetic moment associated with
mineral particles and coal. The microwave heating enhances
the magnetic susceptibility of the iron mineral, thus rendering
it more amenable to the magnetic separation. The effect of
microwave heating on magnetic processing of the pyrite was
investigated 2 , where different size fractions of the pyrite
were heated in a microwave oven at 2.45 GHz frequency
and different power levels. Ability of coal desulfurization by
magnetic separation following microwave heating was also
investigated 3 . The microwaves were found as an effective
method to selective heating of pyrite in the coal causing the
formation of pyrrhotite. It was stated that pyrrhotite could be
removed by low-intensity magnetic separation. 4–6
Experimental
C o a l S a m p l e C h a r a c t e r i z a t i o n
In this study, five different coal samples were used. They
were ground to less than 3 mm and the representative samples
were prepared. The results of analyses of the total sulphur
content are listed in Table I.
M i c r o w a v e a n d C l a s s i c a l H e a t i n g
The microwave heating of investigated coal samples
was realized in the microwave oven Whirlpool AVM 434
and Panasonic nn 5251 B with maximum power of 900 W,
adjusted for the laboratory purposes for continuos temperature
measuring of heated material. The temperature was measured
using the contactless thermometer Raynger MX4 in the
range 30–900 °C. The classical heating of coal in the mufle
oven was realized as well.
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Table I
Total sulphur content in the coal samples
Locality Grain size [mm] S tot [%]
Handlová (SR) –3 1.5
nováky (SR) –3 3.0
Cígeľ (SR) –3 2.27
1–3 5.35
Sokolov (CR) 0.07–0.5 6.85
–0.07 7.52
1–3 0.5
0.5–1 0.5
Donbas (R) 0.2–0.5 0.49
0.07–0.2 0.53
–0.07 0.52
M a g n e t i c S e p a r a t i o n
The magnetic separation of the coal samples was carried
out by means of a roll-type electromagnetic separator Mechanobr,
type 138 T-SEM, intended for dry separation.
M i c r o w a v e R a d i a t i o n a n d M o l t e n
C a u s t i c L e a c h i n g – R M C L
A mixture of 15 g coal + 15 g naOH + 10 ml H 2 O was
used as an input to microwave oven operating in nitrogen
atmosphere. Microwave desulphurizastion of coal was realised
according to the Scheme 1.
Scheme 1
The RMCL (Radiation and Molten Caustic Leaching)
desulphurization of coal
Results
M a g n e t i c S e p a r a t i o n o f C o a l
Coal sample of the grain size 0.05–0.2 mm was heated
before magnetic separation in the microwave oven for
10 minutes at the power 900 W and frequency 2.45 GHz. The
results of the magnetic separation after microwave radiation
are listed in Table II.
The magnetic separation of the coal sample was ineffective
for our conditions.
T h e M o l t e n C a u s t i c L e a c h i n g o f
C o a l
Effect of ratio of NaOh and coal
The effect of ratio of naOH and coal from the Cígeľ
locality after the microwave radiation (2.5 minutes) on reduction
of the total sulphur content is displayed in Fig. 1.