CALCINATION OF LIMESTONE METE 159: PYROMETALLURGICAL LABORATORY
ABSTRACT
The decomposition of calcium carbonate to form calcium oxide and carbon dioxide gas was done by calcining it at 900 °C. Sample preparation was carried out by screening the limestone at different numbers of mesh namely at -20 esh! -"0 mesh! -#0 mesh! -$20 mesh and -200 mesh. 2 trials were prepared for each mesh weighing $0 grams per sample. The effect of particle si%e in calcining was analy%ed and the results are for for 20 mesh the a&erage weight loss is $.'( grams! in "0 mesh the a&erage weight loss is $.)$# grams! in #0 mesh being $.'"# grams! in $20 mesh being $.(( grams and finally in 200 mesh the a&erage weight weight loss is $.9' grams. *s the data suggests! an increase in weight loss is associated with finer particle si%e.
INTRODUCTION Calc Calcin inat atio ion n is deri derive ved d from from the the Lati Latin n word word calcinare which means to burn lime in which the decomp decomposi ositio tion n of calciu calcium m carbon carbonate ate to calciu calcium m oxide and carbon dioxide takes place i.e. a thermal treatment to bring about a thermal decomposition. The temperature applied on the heating of the solid is below its melting point to produce a condition of thermal thermal decomposit decomposition ion or phase transition transition other than than meltin melting g or fusing fusing.. In the case of limest limestone one calcination, the chemical process is: CaCO
' kilogram of limestone was washed with distilled water to remove an% impurities present. It was then sun dried to remove the moisture in the limestone. It was then ground and screened at different mesh namel% 1"- mesh, 12- mesh, 13- mesh, 1'"- mesh and 1"-- mesh. " trials were then prepared each weighi weighing ng '- grams grams of limest limestone one.. Calcin Calcining ing was then commenced at 4-- ℃.
Preparation of samples Weighing 10 grams of sample per trial
CaO ! CO " #g$
Calcining at 900 ℃ The reaction presented above is highl% endothermic which re&uires .'( )* of heat input to produce ' tonn tonnee of lime lime and and the the calc calcin inat ation ion begi begins ns at a temperature of +- C.
Recording the nal weight +lowsheet $. This This figu figure re show showss the the proc proces esss in calcining.
OBJECTIVES OF THE STUDY This experiment experiment aims to familiari/e familiari/e students students the thermal decomposition of limestone and stud% the effects of temperature in calcining.
ESULTS R ESULTS
AND DISCUSSION
The data gathered is summari/ed in table ' where the weight before and after calcining is presented.
SIGNIFICANCE OF THE STUDY The The stud% stud% in lime limest ston onee and and its its deco decomp mpos osit itio ion n process is of importance due to its wide usage. Lime can be used in the construction industr% as well as in cement making. 0speciall% in metallurg%, calcium carbonate is used for slag formation and mainl% in steel manufacture.
MATERIALS AND METHODS Materia! a"# E$%i&'e"t:
The The mate materi riaals and and e&ui e&uipm pmeent use used in the the expe experi rime ment nt were were mort mortar ar and and pest pestle le,, scre screen en,, crucible, electrical balance, limestone and furnace. Pr()e#%re:
5t. of crucible #grams$
5t. of sample
Trial ' Trial "
".(" "3.4
'-.-'-.--
'.4" 2.-+
'.+'.(
Trial ' Trial "
"".( "".'"
'-.-'-.--
'.-" -.3-
'.(' '.("
Trial ' Trial "
"2.2 "2.-4
'-.-' '-.-'
".+ "."+
'.(( '.
Trial ' Trial "
'4.-"3.'
'-.- '-.-
"+.-+ .34
'.4( '.-
Trial ' Trial "
"2.-3 "+.+2
'-.-'-.--
".- 3.++
'.4+ '.4+
#grams$
5t. after firing
5t. loss #grams$
#grams$
1"mes h 12mes h 13mes h 1'"mes h 1"-mes
Calcination of limestone. limestone . Submitted to! ,nstructor. 6age 1 of *
h Table $. 7ummar% of data 8s the limestone is heated strongl% at 4-- ℃, thermal decomposition takes place wherein it breaks down to form calcium oxide and carbon dioxide is released. 8s presented in the data it can be seen that the maximum calcination rate is achieved when CaCO particle si/e is finer.
6lotting the average weight of each samples with different mesh, an increasing trend can be observed that particle si/e has an effect in the decomposition of limestone. The weight remained in the sample can be assumed to be CaO but not purel% since other impurities can account to the remaining weight of the sample.
CONCLUSION AND R ECOMMENDATION The average weight loss of samples per mesh is calculated. 9or 1"- mesh the average weight loss is '.+ grams, in 12- mesh the average weight loss is '.('3 grams, in 13- mesh being '.+23 grams, in 1'"- mesh being '. grams and finall% in 1"-mesh the average weight loss is '.4+ grams. 8 graph is shown in 9igure ' to further visuali/e the trend for var%ing the particle si/e of limestone. It should be noted that the time of calcining has been assumed to be constant since all samples were calcined at the same time and was retrieved from the furnace simultaneousl%.
9rom the activit%, it can be seen that particle si/e affects the formation of CaO with coarser particles forming more CaO but it is not entirel% true since the maximum calcination rate is not achieved when coarser particles are calcined. ore data could have been anal%/ed if time was varied with samples so as to see if an optimum time can be determined for maximum formation of CaO. 8lso, CO" partial pressure could have been explored regarding if it affects the decomposition process.
