A Study on the Manufacture of Clinker Using Low Grade Limestone and Waste Paper Sludge

Resources Processing 51:163–168 (2004) RESOURCES PROCESSING Original Paper

Charn-Hoon PARK1, Chung-Bong OH1, Hyun-Seo PARK1, Ki-Suk HAN2 and Ji-Whan AHN2

1Inha University, Incheon 402-751, Korea 2Korea Institute of Geoscience & Mineral Resources

Abstract This study was carried out to manufacture portland cement clinker using low grade limestone and waste paper sludge. Waste paper sludges were added to supply CaO component in low grade limestone, because low grade limestone contains relatively poor CaO. The cement raw materials such as limestone, clay and iron-ore were obtained in Ssangyong cement in Donghae, waste paper sludge in Samil paper. Composition and texture of raw materials and cement mineral phases were investigated by XRF, XRD and DTA etc.. Portland clinker was made as follows. Modulus of mixture of raw materials was fixed in LSF = 94.0, SM = 2.4 and IM = 1.7. Raw materials are crushed, mixed and ground to fine powder, then put into furnace where it is heated to burning temperature. In here, CaF2 as a fluxing agent was used to facilitate burning. From the experimental results it appears CaF2 promotes that produces C2S at relatively low temperature of 1,100°C. Cement minerals were produced as C2S at 1,100°C and C3S at 1,200°C. Also it was found that when water is added to cement minerals, there follows formation of cement hydrates such as C-S-H and ettringite.

Introduction Fe2O3(2~4%) and the minor composition of MgO, alkali, SO3 are less than 10% [4]. Portland cement is manufactured by sintering Also, high grade limestone had a sufficiency of the mixture of raw materials composed of CaO, CaO is used as raw materials for manufacturing SiO2, Al2O3, Fe2O3 mainly [1]. clinker with enough strength revelation. Relative- Portland cement is produced by the high tem- ly low grade limestone containing poor CaO can perature reaction of a lime-bearing material with not produce sufficient C3S and C2S. The waste pa- one containing silica, alumina and ferrous materi- per sludge contains the most quantity of CaO als. The product, which is known as clinker, is component. afterwards ground with gypsum to give cement Modulus of raw mixtures is difficult to control, [2,3]. because low-grade limestone contains low value The main mineral phases in the clinker are C3S of CaO and high value of SiO2. (tricalcium silicate), C2S (dicalcium silicate), C3A Therefore in this study, the formation tempera- (calcium aluminate) and C4AF (tetracalcium alu- ture, mineral composition and crystal structure of minoferrite). These four compounds are formed cement minerals produced when manufacturing by burning reaction of CaO, SiO2, Al2O3 and clinker using low grade limestone and waste pa- Fe2O3 components at high temperature. Quality of per sludge are investigated as a basic study for the cement is determined by composition ratio of utilization and recycling on the two materials the four compounds. The main composition is above mentioned. CaO(60~65%), SiO2(22~24%), Al2O3(4~7%), Experimental

Accepted 8 March 2004 Limestone, clay and iron ore were obtained in

Vol. 51, No. 3 (2004) 163 Charn-Hoon PARK, Chung-Bong OH, Hyun-Seo PARK, Ki-Suk HAN and Ji-Whan AHN Ssangyong cement in Donghae. The waste sludge Results and discussion come out from the manufacturing process of high quality art paper in Samil Paper in Namyangju Characteristics of raw material was also used in this experiment. Table 1 shows The chemical composition of raw materials in the chemical composition of the raw material this study is shown in Table 1. Usually, the mix- samples for clinker. ing ratio of limestone in the raw mixtures of Chemical compositions of the raw mixture Portland cement is 76~80%. However, the mix- for manufacture of Portland cement were fixed ing ratio increases according to the content of in LSF 94.0, SM 2.4 and IM 1.7 and were then impurities, and also because compounding mate- ground together for 8 hours in an attrition mill rials using low grade limestone have a mixing ra- under wet conditions. Raw mixtures were tio of more than 93% limestone, clay decreases formed by pressure of 800 kg/cm2, decarbonat- less than 5%. ed for 1 hour at 1,000°C, and then burned at Specification of raw material minerals is an im- temperatures between 1,000°C~1,500°C by in- portant means of raw material selection and com- crements of 100°C. position ratio decision. Burn ability of the raw We analyzed the composition and the proper- mixtures is an important factor to consider. ties from heating extremely small quantities of Usually, optimum conditions of raw mixture each mineral and that of gap using SEM and EDS cement are when it has the highest burn ability, to investigate the crystal size of main phase and which creates a fine crystalline structure of lime- the composition change of synthesized clinkers. stone and silicate clay mineral with a high surface Synthesized clinkers were ground under 200 area when combined with water. mesh, added with 3% gypsum (CaSO4 · 2H2O) Limestone works because the main mineral and the experiments of hydration reaction on contains calcite or quartz according to produce, the cement materials were carried out. The dolomite, accompanying clay minerals (kaolinite, water/cement ratio of hydration reaction was iolite, etc.), mica minerals (muscovite, biotite, 0.5. The hydrated cement materials were then etc.), chlorite minerals (chlorite groups) and feld- mixed well and cured for 1, 3, 7 and 28 days at spar minerals (microcline) etc., which varies from 23 ± 2°C. Following the hydration reaction of one another due to the deposit accumulation by the curing period, acetone was added for sus- the mother mineral. pension of the hydration reaction and the mix- Limestone contains impurities of SiO2, Al2O3, ture was then stored in a desiccator. Fe2O3, MgO, alkali, etc. SiO2, Al2O3, Fe2O3 of these ingredients are the main components that make up cement mineral. MgO, alkali or others inter-solidified by mineralizer of cement mineral,

Table 1 Analysis of XRF for samples (unit: wt%) high-grade Low-grade waste paper Sample iron-ore clay limestone limestone sludge

SiO2 1.04 5.91 14.68 54.41 1.64 Al2O3 0.43 1.18 1.75 17.69 2.57 Fe2O3 0.14 0.45 71.11 10.38 0.14 TiO2 0.02 0.03 0.23 1.33 4.41 MnO0.010.130.970.290.01 CaO 52.23 46.70 5.36 1.30 54.31 MgO1.983.353.361.840.64 K2O 0.130.480.564.500.02 Na2O < 0.06 < 0.07 < 0.08 < 0.06 < 0.07 P2O5 0.01 0.05 0.23 0.15 0.07 L.O.I 43.71 41.40 1.65 8.05 35.71 Total 99.76 99.75 99.98 100.00 99.59

*Fe2O3: Total Fe L.O.I: Loss on ignition * LSF (Lime Saturation Factor): 100CaO/(2.8SiO2 + 1.18Al2O3 + 0.65 Fe2O3) SM (Silica Modulus): SiO2/(Al2O3 + Fe2O3) IM (Iron Modulus): Al2O3/Fe2O3

164 RESOURCES PROCESSING A Study on the Manufacture of Clinker Using Low Grade Limestone and Waste Paper Sludge creating a profitable effect that promotes reactivi- grade of the limestone. ty. However, the content of these ingredients is Use raw material ground and measured so that limited and shows considerable difference be- 90 µm sieve residue may become 18 ± 1.0%. DTA tween each other according to deposit. as shown in Fig. 2. The CaO content case of sludge is 55%, the DTA was measured to compare the decar- L.O.I. pulp ingredient exceeds 30%, the SiO2, bonation reaction state. Decarbonation feed- Al2O3, and Fe2O3 that are the remainder of the ce- back did not greatly change according to the ment clinker raw material exist as impurities and grade of limestone. Most limestone have a TiO2 exists at about 4%. maximum endothermic peak between 800°C Fig. 1 shows the polarizing microphotographs while heat absorption process progresses from of limestone. In the case of low grade limestone 700°C. Further, they show the tendency that as compared to high grade, the range of calcite definite point temperature of decarbonation re- mineral was small, while that of crystal grain was action becomes lower in 20°C interior and exte- relatively large and dolomite was significant. rior in case of low grade limestone. Differences in crystal structure greatly affect In the case of waste sludge, decarbonation reac- the burnability of cement raw mixture. tion initiated at 680°C and reached a maximum Low grade dolomitic limestone having MgO endothermic peak at 790°C. This agrees almost impurity, that is a particle of CaO formed during completely with the heat absorption process of cement mixing raw material burning, will be rela- limestone and it seems that endothermic reaction tively big and may greatly affect the beginning of much calcite in sludge. temperature of formation and quantity of cement The temperature difference between the endo- mineral that is formed during burning. thermic reaction of low grade limestone and Reactivity of the raw mixture is influenced waste paper sludge lowers the dissolution activa- greatly in pyrolysis, a special quality of lime- tion energy of limestone, because particle size is stone. The pyrolysis characteristic of limestone is small and low grade limestone contains many greatly influenced by particle size of calcite crys- impurities. tal, crystal shape thatis characteristic of limestone As a result, the decarbonation process becomes itself and outside impurities such as SiO2, Al2O3, simplified, because the particle size of limestone Fe2O3, etc. as well as the existence state of accom- is relatively microscopic in the case of waste pa- panying minerals. per sludge. Therefore, in this experiment, impurities con- Refer to XRD patterns of Fig. 3 for differences tained in limestone and clay mixture in raw mate- between high quality and low quality of the impu- rial composition have been regarded. Ingredients rity ingredient contained to limestone. Low quali- of iron ore as impurities of all limestones, and dif- ty has been compared to high quality and appears ferential thermal analysis have been determined relatively great of all diffraction intensity of to investigate whether they cause some effect in quartz and calcite, and appearing muscovite and the pyrolysis of their entire mixture materials be- peak of dolomite. Specially, dolomite is that Mg cause their contents are changed according to the is substituted to calcite, therefore calcite mineral

Fig. 1 Microphotographs of limestone sample (Cross nicol, × 50)

Vol. 51, No. 3 (2004) 165 Charn-Hoon PARK, Chung-Bong OH, Hyun-Seo PARK, Ki-Suk HAN and Ji-Whan AHN

Fig. 2 DTA curves of high-low grade limestone and waste paper sludge decreases relatively compared to high quality. Al- Fig. 3 XRD patterns of high-low grade Limestone so, peak of SiO2 is seen that is caused in content of quartz. Al2O3, Fe2O3, etc. from materials that help dis- From fig. 4, it shows that clay mineral is main- solution formation. C3S is formed at a low tem- ly composed of illite containing small quantities perature of 100°C. Than case that do not add of muscovite and quartz. Iron ore is magnetite and fluorite as appear to XRD chart of Fig. 6 when hematite that is accomplishing Fe2O3 in main in- added fluorite that is flux in this experiment. gredients by main composition mineral, and C2S and CaO of C3S exist when liquid phase quartz is looked by appearing by impurities of appears by solid solution reaction. This receives argillaceous materialthat exist between crack. the effect of viscosity and is thought that forma- Formation of cement mineral tion of C3S quickens because the liquid phase 2+ Fig. 5 shows how clinker was analyzed and speed of CaO and C2S and diffusion of Ca be- burned at temperatures ranging from 1,100 come fast once viscosity is decreased. The decline ~1,400°C to see the formation state of cement of foremost dissolution appearance temperature mineral that mixed low grade limestone, waste and dissolution amount increase and dissolution paper sludge, clay, iron ore and fluorite by viscosity with the addition of flux decreases. XRD patterns. The main mineral phases were Hydration of cement mineral C3S, β-C2S, C3A, C4AF and free-CaO. The major composition minerals of portland CaO was formed at 1,100°C and existed to cement are solid solutions. Its main ingredients 1,200°C. C3S was formed at 1,200°C. β-C2S are C3S, C2S, C3A and C4AF. C3S and C2S are showed that crystal grows up to 1,400°C after minerals that have an effect on strength, the major being formed at 1100°C. Formation of free- property of cement, and on the quality of cement. CaO disappears at 1,200°C. Free-CaO reacts In particular, C3S contributes greatly to the early with C2S and then forms by C3S. strength of cement and C2S contributes greatly to The method used to form C3S in low temper- the later strength, respectively. C3A and C4AF are atures is a practical use of mineralizers and formed by intersititial mineral in space of calcium flux. Representative mineralizers are CaF2, silicate mineral(C3S, C2S), and act on setting time

166 RESOURCES PROCESSING A Study on the Manufacture of Clinker Using Low Grade Limestone and Waste Paper Sludge as a major factor in the hydrated reaction of cement. Fig. 7 shows sintered clinker hydrated with 3% gypsum to obtain the cement, which were then hydrated in 20°C for 3, 7 and 28 days, respectively. After 3 days, needle-shaped ettringite were showned. In case of 7 and 28 days, calcium silicate hydrate (CSH) is well-developed and forms in a pillar-shape.

Fig. 5 XRD patterns of sintered clinkers from raw mixtures without CaF2 at 1,100~1,400°C A: low grade limestone + iron rock + clay + waste paper sludge

Fig. 6 XRD patterns of sintered clinkers from raw mixture with CaF2 at 1,100~1,400°C B: low grade limestone + iron rock + clay + waste paper sludge + CaF2

Fig. 4 XRD Patterns of raw material for making clinker

Fig. 7 Scanning electron micrographs for hydrates of clinker at various curing time

Vol. 51, No. 3 (2004) 167 Charn-Hoon PARK, Chung-Bong OH, Hyun-Seo PARK, Ki-Suk HAN and Ji-Whan AHN Conclusion 4. It was confirmed that can synthesize cement minerals in lower temperature, when 5~7% waste 1. Low grade limestone contains CaO(46.70%), paper sludge and 1% CaF2 are added in low grade SiO2(5.91%), Al2O3(1.18%), Fe2O3(0.45%), limestone. MgO(3.35%), and waste paper sludge contains CaO(54.31%), SiO2(1.64%), Al2O3(2.57%), Acknowledgement Fe2O3(0.14%), MgO(0.64%). Waste paper sludge contains high grade of CaO and low ingredient of Authors express appreciation for support of this SiO2 in compare with low grade limestone. Mod- research by grant of Inha University. ulus of mixture of raw materials was fixed in LSF = 94.0, SM = 2.4 and IM = 1.7. References 2. Cement minerals were produced as C2S at 1,100°C and C3S at 1,200°C. β-C2S showed that 1. Investigation Report of Waste Occurrence crystal grows up to 1,400°C after being formed at and Processing Situation in Paper Industry, 1100°C. Formation of free-CaO disappears at Korea Paper Industry Association, 1996 1,200°C. Free-CaO reacts with C2S and then 2. Yas-O Arai, Material Chemistry of Cement, forms by C3S. Dainippon Dosho, P. 132, 1984 3. When did not add fluorite(CaF2) that is easy 3. F.W. Locher, Low Energy Cement, Proc. 8th burning material, C2S formed rapidly by impuri- Inter. Cong. Chem. Cement. Vol. 1, P. 57, ties was formed continuously growing crystal to 1986 1,400°C. Therefore it was known that C3S influ- 4. Robert Herman Bogue, The Chemistry of enced on strength of cement mineral was not syn- Portland Cement, P. 205 thesize sufficiently.

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