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Prediction of the degree of thermal breakdown of limestone : a case study of the Upper Ordovician Boda Limestone, Siljan district, central Sweden

Olsson, Håkan LU (2012) In Dissertations in Geology at Lund University GEOR02 20102
Department of Geology
Abstract
Quicklime (CaO) is an important geological resource with a wide variety of industrial uses. It is a base chemical produced from the burning of limestone or dolomite. This process is referred to as calcination, during which the limestone is heated to temperatures of 900 °C or higher, resulting in the discharge of CO₂, leaving a yield of quicklime. The formula can be written as follows:
Limestone: CaCO₃ + heat → CaO + CO₂
Dolomite: CaMg(CO₃) ₂+ heat → CaO + MgO + 2CO₂
During calcination, a pure limestone looses about 44% of its weight, while a pure dolomite looses 48%. The amount of silica, alumina and other impurities of the original rocks is therefore near doubled. Calcination may also result in a notable loss of strength leading to... (More)
Quicklime (CaO) is an important geological resource with a wide variety of industrial uses. It is a base chemical produced from the burning of limestone or dolomite. This process is referred to as calcination, during which the limestone is heated to temperatures of 900 °C or higher, resulting in the discharge of CO₂, leaving a yield of quicklime. The formula can be written as follows:
Limestone: CaCO₃ + heat → CaO + CO₂
Dolomite: CaMg(CO₃) ₂+ heat → CaO + MgO + 2CO₂
During calcination, a pure limestone looses about 44% of its weight, while a pure dolomite looses 48%. The amount of silica, alumina and other impurities of the original rocks is therefore near doubled. Calcination may also result in a notable loss of strength leading to fragmentation of the quicklime and formation of very fine-grained powdery material, so called ‘fines’. In most areas of use, high amounts of impurities and fines are undesirable. In the present case study, three drillcores (KBH 1, 2 and 3), retrieved by Svenska Mineral from the Boda Limestone in the Siljan district, Central Sweden, have been studied with regard to facies and structure to ascertain the suitability of this limestone for the production of quicklime. The Boda limestone consists of large dome-shaped carbonate mud-mounds. The mounds consist of two members; a core member and a flank member. The core member can be subdivided in two overall facies; a red mudstone facies, which is present in all three cores, and a brown core facies only found in KBH 2. The flank member, which consists of pelmatozoan wackestone and packstone, can be found in KBH 1 and 2, while KBH 3 almost entirely consists of the red mudstone. In order to correlate limestone composition with percentage of fines after calcination, the amount of fractures, the presence of stromatactis, and the over-all core-recovery were described for each core. Following this analysis, nearly 200 samples were selected from KBH 1 and 2 and subjected to calcination and mechanical force in order to simulate the industrial handling and production of CaO. The produced fines where then weighted for each sample and plotted against the physical properties of each core. The results show a clear correlation between facies and the amount of fines. The red mudstone facies gave the lowest overall values, predominantly less than 10% fines. The brown core facies has more varying values, ranging from 10-60%. The flank member ranges between 20-80%. Surprisingly, the fracture frequency seems to have little impact on the amount of fines after calcination. The presence stromatactis did not have an ad-verse effect on fines either. It can be concluded that the planning for an optimal use of an economically important limestone occurrence is greatly facilitated by detailed knowledge regarding the facies of the limestone and other properties such as chemistry, mineralogy of impurities and micro-textures. (Less)
Abstract (Swedish)
Populärvetenskaplig sammanfattning
Kalksten är en av våra viktiga geologiska resurser och har genom historien använts till byggnadsmaterial, jordbruk och inom modern industri. Kalksten i alla dess former har varit en viktig del av människans kulturella och teknologiska utveckling. Ett av alla dess användningsområden är som flussmedel vid bearbetning av järnmalm; bränd kalk tillsätts när malmen smälts och binder då till de ämnen i malmen man vill separera från järnet. Detta är då främst kisel- och aluminiummineral. Bränd kalk är kalk som blivit upphettad till sådana temperaturer att CO₂ avges från CaCO₃. Den kvarvarande CaO är reaktiv och binder lätt till CO₂ och vatten. När CaO, på engelska kallad ”lime”, reagerar med vatten bildas släckt... (More)
Populärvetenskaplig sammanfattning
Kalksten är en av våra viktiga geologiska resurser och har genom historien använts till byggnadsmaterial, jordbruk och inom modern industri. Kalksten i alla dess former har varit en viktig del av människans kulturella och teknologiska utveckling. Ett av alla dess användningsområden är som flussmedel vid bearbetning av järnmalm; bränd kalk tillsätts när malmen smälts och binder då till de ämnen i malmen man vill separera från järnet. Detta är då främst kisel- och aluminiummineral. Bränd kalk är kalk som blivit upphettad till sådana temperaturer att CO₂ avges från CaCO₃. Den kvarvarande CaO är reaktiv och binder lätt till CO₂ och vatten. När CaO, på engelska kallad ”lime”, reagerar med vatten bildas släckt kalk, CaOH eller ”quicklime”.
För att den brända kalken ska vara ett så effektivt flussmedel som möjligt krävs att den kan tillsättas som större stycken snarare än ett finfördelat pulver. Detta medför större krav på den kalksten som används som ursprungsmaterial till den brända kalken. Den måste kunna stå emot upphettningsprocessen och mekanisk påfrestning både före, under och efter bränningen. Produktionskostnaden för bränd kalk är också väldigt hög; kalken måste hettas upp till över 900 °C tillräckligt länge för att all CO2 skall avges. När detta sker minskar massan med 44 % då CO₂ övergår till gasform. Produceras då större mängder oanvändbart finmaterial vid bränningen går mycket material och energi gott till spillo, såväl som att stora mängder CO₂ släppts ut.
I den här studien har tre borrkärnor (KBH 1-3) undersökts, upptagna av Svenska Mineral från Bodakalkstenen i Siljansringen, Sverige. Undersökningarna har omfattat studier av facies och strukturer för att avgöra huruvida kalkstenen lämpar sig för produktion av bränd kalk. Bodakalkstenen består av större domformade rev. Dessa kan delas in i två enheter, en kärnenhet och en flankenhet. Kärnenheten kan i sin tur delas in i röd lerkalksfacies och brun kärnfacies som bara påträffats i KBH 2. Flankenheten består av rasmaterial, främst i form av fragment från sjöliljor och lerkalk. Denna påträffas i båda KBH 1 och 2 medens KBH 3 utgörs av mestadels röd kalkler. Andelen fin-material som bildats vid bränning har korrelerats med facies, sprickor, stromatactis strukturer och sammanhållningen av den upphämtade kärnan. Nära 200 prov togs från KBH 1 och 2, och utsattes för bränning, följt av mekanisk påverkan för att simulera industriell behandling. Finmaterialet som då producerats har vägts för vart prov och plottats mot kärnornas egenskaper. Resultaten visar på en tydlig korrelation mellan facies och finmaterial. Den röda kalkleren gav generellt mindre än 10 % finmaterial medens den bruna kärnfacien gav mellan 20 och 80 % och flank-enheten gav mellan 20 och 80 %. Däremot hittas ingen korrelation mellan hög sprickighet och högre procent fin-material. Stromataktis strukturer verkar ha en benägenhet att sänka andelen finmaterial något. Vid planeringen av brytning av liknade kalkförekomster kan en bättre förståelse av facies och andra faktorer vara av stor ekonomisk vikt då det kan påvisa förekomstens lämplighet. (Less)
Please use this url to cite or link to this publication:
author
Olsson, Håkan LU
supervisor
organization
alternative title
Att förutse det termala söderfallet av kalksten : en studie av den överordoviciska Bodakalkstenen, Siljansringen, centrala Sverige
course
GEOR02 20102
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Boda, quicklime, lime, limestone, calcining, Siljan, fluxstone, ore, kalk, kalksten, bränd, släckt, CaO
publication/series
Dissertations in Geology at Lund University
report number
312
language
English
id
3047018
date added to LUP
2012-09-05 10:57:28
date last changed
2012-09-05 11:17:00
@misc{3047018,
  abstract     = {Quicklime (CaO) is an important geological resource with a wide variety of industrial uses. It is a base chemical produced from the burning of limestone or dolomite. This process is referred to as calcination, during which the limestone is heated to temperatures of 900 °C or higher, resulting in the discharge of CO₂, leaving a yield of quicklime. The formula can be written as follows: 
Limestone: CaCO₃ + heat → CaO + CO₂ 
Dolomite: CaMg(CO₃) ₂+ heat → CaO + MgO + 2CO₂ 
During calcination, a pure limestone looses about 44% of its weight, while a pure dolomite looses 48%. The amount of silica, alumina and other impurities of the original rocks is therefore near doubled. Calcination may also result in a notable loss of strength leading to fragmentation of the quicklime and formation of very fine-grained powdery material, so called ‘fines’. In most areas of use, high amounts of impurities and fines are undesirable. In the present case study, three drillcores (KBH 1, 2 and 3), retrieved by Svenska Mineral from the Boda Limestone in the Siljan district, Central Sweden, have been studied with regard to facies and structure to ascertain the suitability of this limestone for the production of quicklime. The Boda limestone consists of large dome-shaped carbonate mud-mounds. The mounds consist of two members; a core member and a flank member. The core member can be subdivided in two overall facies; a red mudstone facies, which is present in all three cores, and a brown core facies only found in KBH 2. The flank member, which consists of pelmatozoan wackestone and packstone, can be found in KBH 1 and 2, while KBH 3 almost entirely consists of the red mudstone. In order to correlate limestone composition with percentage of fines after calcination, the amount of fractures, the presence of stromatactis, and the over-all core-recovery were described for each core. Following this analysis, nearly 200 samples were selected from KBH 1 and 2 and subjected to calcination and mechanical force in order to simulate the industrial handling and production of CaO. The produced fines where then weighted for each sample and plotted against the physical properties of each core. The results show a clear correlation between facies and the amount of fines. The red mudstone facies gave the lowest overall values, predominantly less than 10% fines. The brown core facies has more varying values, ranging from 10-60%. The flank member ranges between 20-80%. Surprisingly, the fracture frequency seems to have little impact on the amount of fines after calcination. The presence stromatactis did not have an ad-verse effect on fines either. It can be concluded that the planning for an optimal use of an economically important limestone occurrence is greatly facilitated by detailed knowledge regarding the facies of the limestone and other properties such as chemistry, mineralogy of impurities and micro-textures.},
  author       = {Olsson, Håkan},
  keyword      = {Boda,quicklime,lime,limestone,calcining,Siljan,fluxstone,ore,kalk,kalksten,bränd,släckt,CaO},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Prediction of the degree of thermal breakdown of limestone : a case study of the Upper Ordovician Boda Limestone, Siljan district, central Sweden},
  year         = {2012},
}