UTILIZATION OF ALUMINIUM PROCESSING WASTE AS RAW MATERIALS IN THE MANUFACTURE OF CEMENT

Transcription

1 UTILIZATION OF ALUMINIUM PROCESSING WASTE AS RAW MATERIALS IN THE MANUFACTURE OF CEMENT M Pareek, Digvijay Singh, D Yadav*, S K Chaturvedi* and M M Ali* Century Metal Recycling Pvt. Ltd., Palwal, Haryana * National Council for Cement and Building Materials, Ballabgarh, Haryana, Abstract In the course of making aluminium alloys by melting aluminium scraps in furnaces, huge quantity of dross gets generated as a bye product. The dross is a mix of aluminium & alumina. In order to recover aluminium from dross, it is processed through two routes namely Hot dross processing and Cold dross processing. In case of Hot dross processing, the material is churned along with exothermic reaction leading to entrapped aluminium getting liquidified & finally getting separated. The remains after aluminium redemption is pre-dominantly alumina. Similarly in case of Cold dross processing, it is taken out for alloy making furnace. The cooled dross is pulverized. The alumina gets powdery in the process of pulverization. However aluminium remains in coarse granular form. After pulverizing, dross is sieved. As a result, powder alumina gets separated from aluminium. Generation of dross at present is of the order of MT per month at various units of CMR. The chemical analysis of dross generated indicated that the alumina content varied in the range of 40-95% depending upon batch/source of aluminium scrap. Considering the potential of this material for use as raw materials in cement manufacture, NCB undertook the investigations for its use as raw materials on sponsorship basis. The paper highlights the complete characterization of various quality of powder generated at their units in four locations, their utilization in cement making and quality of clinker / cement thus produced. Generation of Aluminium waste In the course of making aluminium alloys by melting aluminium scraps in furnaces, huge quantity of dross gets generated as a bye product. The dross is a mix of aluminium & alumina. In order to recover aluminium from dross, it is processed through two routes namely Hot dross processing and Cold dross processing. In case of Hot dross processing, the material is churned resulting in exothermic reaction leading to entrapped aluminium getting liquidified & finally getting separated. The remains after aluminium redemption is pre-dominantly alumina. Similarly in case of Cold dross processing, it is taken out for alloy making furnace. The cooled dross is pulverized. The alumina gets powdery in the process of pulverization. However aluminium remains in coarse granular form. After pulverizing, dross is sieved. As a result, powder alumina gets separated from aluminium. Generation of dross at present is of the order of MT per month at various units of CMR. Material Characterisation Chemical Analysis of Aluminium Wastes The chemical analysis indicated that in case of Alumina waste samples, CP-AL, CP-POD, IDSM- 1AL and IDSM-2AL, the Al2O3 and Fe2O3 content varied in the range of and percent respectively. The MgO content was found to vary between percent. The samples also contained Na2O, K2O and chlorides in the range of , and 1.68-

2 7.26 percent respectively. Further, the samples of IDSM process gained weight on ignition and the same was 0.70 and 4.30 percent respectively for IDSM-1AL and IDSM-2AL. The detailed chemical analysis of these alumina waste samples are presented in Table 1. Table 1 Chemical Analysis of Alumina Waste Samples Oxides, % CP-AL CP-POD IDSM 1AL IDSM 2AL Loss on ignition (+)0.70 (+)4.30 SiO Fe 2 O Al 2 O MgO SO Na 2 O K 2 O TiO Cl Reactive silica The samples were subjected to trace element analysis using state of art ICP and the results are as given below in Table 2. The results obtained indicated that the various trace elements present in the aluminium wastes were barium, cadmium, chromium, copper, cobalt, manganese, molybdenum, nickel, lead, zinc, vanadium and strontium. The concentration of these trace elements was very low. Beryllium was found only in IDSM samples. The concentration of other trace elements such as thallium and selenium, was nil. Table 2 Concentration of Trace Elements present in Aluminium Wastes Element CP-AL CP-POD IDSM 1AL IDSM 2AL Ba Be NIL NIL Cd NIL Co NIL Cr Cu Mn Mo Ni Pb Se NIL NIL NIL NIL Sr Thallium NIL NIL NIL NIL Zn V The chemical analysis of Limestone and additives used in the study are as given in Table 3 below:

3 Table 3 Chemical Analysis of Limestone and Additive Samples Oxides, % LS - 1 LS - 2 BXT ISLD LOI SiO Fe 2 O Al 2 O CaO MgO SO 3 Nil Nil Nil Nil Na 2 O K 2 O Cl Free Silica Natural moisture XRD Analysis of Aluminium waste Samples The results of XRD investigation of Aluminium waste CP-AL indicated that the mineral phases were halite, sylvite, perovskite, Mg-Al spinels, corundum, quartz, fayalite and talc (Fig 1). Similarly, the results of XRD investigation of Aluminium waste CP-POD indicated that the mineral phases were halite, sylvite, perovskite, Mg-Al spinels, corundum, quartz, fayalite, hematite and talc (Fig 2). Fig 1: XRD pattern of CP-AL Fig 2: XRD pattern of CP-POD Fig 3: XRD pattern of IDSM 1AL Fig 4: XRD pattern of IDSM 2AL

4 The results of XRD investigation of Aluminium waste IDSM-1AL indicated that the mineral phases were halite, sylvite, perovskite, Mg-Al spinels, corundum, fersilicate, quartz fayalite, SiC and talc (Fig 3). The results of XRD investigation of Aluminium waste IDSM-2AL indicated that the mineral phases were halite, perovskite, Mg-Al spinels, corundum, quartz, fayalite, montmorrilonite, pyrophilite and talc (Fig 4). The summary of results of XRD investigation of limestone and additives are presented in Table 4 below: Table 4 XRD Investigations of Limestone and Additive Samples Sample Minerals identified Limestone, LS-1 Calcite-CaCO 3, Quartz-SiO 2, Montmorillonite-15A- Ca 0.2 (Al,Mg) 2 Si 4 O 10 (OH) 2.4H 2 O Limestone, LS-2 Calcite-CaCO 3, Quartz-SiO 2, Aragonite-CaCO 3, Bauxite, BXT Iron, sludge,isld Gibbsite-Al(OH) 3, Calcite-CaCO 3, Hematite-Fe 2 O 3, Anatase-TiO 2, Goethite-FeO(OH), Kaolinite-Al 2 Si 2 O 5 (OH) 4, Quartz-SiO 2, Magnetite-Fe3O4, Goethite-FeO(OH), Hematite-Fe2O3 and Quartz- SiO 2, The MODAL composition and granulometric analysis of glass grains present in alumina wastes samples were evaluated by optical microscope and the results are provided in Table 5 and Table 6 respectively. IDSM-1AL ( 50x-x-nicols) IDSM-2AL( 50x-x-nicols) CP-AL.( 50x-x-nicols) CP-POD ( 50x-x-nicols) Optical Micrographs of Various Alumina wastes

5 Table 5 MODAL Composition of Alumina Wastes Samples Sample Minerals Present (%) Glass Semi Glass Opaque Minerals IDSM-1AL IDSM-2AL CP-AL CP-POD Experimentation Table 6 Granulometric Analysis of Glass Grains present Sample Granulometry (µm) MIN. MAX. AVERAGE IDSM-1AL IDSM-2AL CP-AL CP-POD Raw Mix Designing using CAW-C Considering the content of chloride in various aluminium wastes, materials namely IDSM-2AL, IDSM-1AL and CP-POD were considered appropriate and mixed in the ratio of 50:25:25 by weight and referred as composite alumina waste, CAW-C and the same were used as cement raw material by replacing alumina bearing additives in raw mix. A number of theoretical raw mixes were designed using two qualities of limestone and additives such as bauxite and iron sludge as control raw mixes and designing another set of raw mixes replacing CAW-C with source of Alumina namely bauxite. While designing these raw mixes, the various quality parameters such as modull values, clinker phases, liquid content, etc. were varied in close and controlled range for the purpose of comparison and drawing logical conclusions. Out of these raw mixes, one raw mix was selected as control raw mix, namely RM-C and 3 raw mixes replacing bauxite with CAW-C were selected for investigations. The coal ash absorption was uniformly kept at 1.50 percent level in all the raw mixes. The designe parameters are presented in Table 7 to 10. Table 7 Design Parameters of Raw Mix RM-C Limestone Limestone Iron Bauxite- Coal ash Raw Materials CAG-C* (LS-1) (LS-2) Sludge (BAU) absorption Proportion (%) Composition (%) LOI CaO SiO 2 Al 2 O 3 Fe 2 O 3 MgO SO 3 Na 2 O K 2 O Raw Mix Clinker Modulii Values LSF SM AM Liquid content (%) Raw Mix Clinker Potential Phase C 3 S C 2 S C 3 A C 4 AF Composition (%)

6 Table 8 Design Parameters of Raw Mix RM-1 Raw Materials Limestone (LS-1) Limestone (LS-HG-1) CAG-C* Iron Sludge Bauxite- (BAU) Coal ash absorption Proportion (%) Composition (%) LOI CaO SiO 2 Al 2 O 3 Fe 2 O 3 MgO SO 3 Na 2 O K 2 O Raw Mix Clinker Modulii Values LSF SM AM Liquid content (%) Raw Mix Clinker Potential Phase C 3 S C 2 S C 3 A C 4 AF Composition (%) Table 9 Design Parameters of Raw Mix RM-2 Raw Materials Limestone (LS-1) Limestone (LS-HG-1) CAG-C* Iron Sludge Bauxite- (BAU) Coal ash absorption Proportion (%) Composition (%) LOI CaO SiO 2 Al 2 O 3 Fe 2 O 3 MgO SO 3 Na 2 O K 2 O Raw Mix Clinker Modulii Values LSF SM AM Liquid content (%) Raw Mix Clinker Potential Phase C 3 S C 2 S C 3 A C 4 AF Composition (%)

7 Table 10 Design Parameters of Raw Mix RM-3 Raw Materials Limestone (LS-1) Limestone (LS-HG-1) CAG-C* Iron Sludge Bauxite- (BAU) Coal ash absorption Proportion (%) Composition (%) LOI CaO SiO 2 Al 2 O 3 Fe 2 O 3 MgO SO 3 Na 2 O K 2 O Raw Mix Clinker Modulii Values LSF SM AM Liquid content (%) Raw Mix Clinker Potential Phase C 3 S C 2 S C 3 A C 4 AF Composition (%) * IDSM-1 (25%) + IDSM-2 (50%) +CP-POD (25%) Preparations of Raw Mixes Raw mixes, RM-C, RM-1, RM-2 and RM-3 were prepared by taking weighed quantities of raw materials as per the designs, blending them thoroughly and grinding the mixes to fineness of ~ 10 percent residue on 90 (170 mesh). The residue level is kept ~ 10 percent as against ~ 14 % or more retained on 90 micron as practiced in industry to obtain optimum sintering as the nodules of these mixes are to be fired in a laboratory scale muffle furnace at NCB and as such do not undergo similar processing conditions as in rotary kiln. Nodules of about 1 cm in diameter were prepared by mixing about 12 percent water and were dried in an electric oven at 105 ± 5 C for about 2 hrs before subjecting them to burnability studies. Burnability Studies Burnability studies were carried out on all the raw mixes. The dry nodules were introduced in a laboratory furnace at ambient temperature, which was gradually raised to desired temperatures. The raw mixes were fired at 1350, 1400 and 1450 C with a retention time of 20 minutes. The resultant clinkers, CL-C, and CL-1, CL-2, CL-3 prepared from the raw mixes, were cooled to ambient and their free lime content determined. The results of free lime determination is presented in Table 11. Evaluation of Clinker Produced during Burnability Studies BY XRD The resultant clinker from raw mixes RM-C, RM-1, RM-2 and RM-3 were evaluated to see the development of clinker phases using XRD. The XRD evaluation indicated that clinkers from all the three raw mixes had potential for formation of adequate clinker phases.

8 Table 11 Burnability Studies of Cement Raw Mixes Raw mix no Temperature Free lime % RM-C RM RM RM Optimization of Raw Mix The raw mixes, RM-C, RM-1, RM-2 and RM-3 yielded good clinkers on burning as shown by the respective free lime values at different temperatures. However looking at the overall quality parameters such as modulli values, liquid content, theoretical clinker phases and the results of XRD investigation of clinker nodules formed during burnability studies, it was considered that raw mixes RM-1 was most promising and optimum for further investigation. The control raw mix RM-C was also investigated for comparison with RM-1 which contained CAW-C. Preparation of Bulk Clinker About 10 Kgs. each of raw mixes namely RM-C and RM-1 were prepared by taking weighed quantities of raw materials, viz. the two limestone, additives, CAW-C and coal ash, blending them and grinding them in a ball mill to a fineness of ~ 10 percent residue on 90 (170 mesh) sieve. The nodules were prepared in a pan nodulizer and dried in an electric oven at 105±5 C for 2 hours before introducing in an electric furnace at ambient temperature and firing it at 1400 C for 20 minutes. The resultant ambient cooled clinker designated as CL-C-B and CL-1-B was studied for chemical and mineralogical characteristics. The Ordinary Portland Cement samples (OPC-C-B and OPC-1-B) prepared were evaluated for their performance as per relevant Indian Standard Specification. Evaluation of Bulk Clinkers Chemical Characteristics The chemical analysis of Bulk clinker CL-C-B and CL-1-B were carried out as per Indian Standard Specification, IS: and the results are presented in Table 12. The analysis indicate that clinker CL-C-B contain percent CaO and percent SiO 2. The SO 3 was found to be 0.20 percent. Similarly, the analysis indicated that clinker CL-1-B contained percent CaO and percent SiO 2. The SO 3 was found to be 0.16 percent. Optical Microscopy of Control Clinker, CL-C-B: The clinker phases are moderately developed and in-homogeneously distributed. Majority of alite grains are pseudo hexagonal in shape with broken out line. Triangular, rectangular, lath and needle shaped alite grains are also developed in the clinker. Numerous inclusions are present in alite grains. Majority of alite grains are in the size range of 20 µm to 25 µm. Most of belite grains

9 Table 12 Chemical Analysis of Bulk Clinker CL-C-B and CL-1-B Constituents Bulk clinker Determined (%) CL-C-B CL-1-B LOI SiO 2 Fe 2 O 3 Al 2 O 3 CaO MgO SO 3 Na 2 O K 2 O Cl TiO 2 CaO f are rounded to sub rounded in shape with corroded margins. Belite grains are mostly present as clusters. Fine globular grains of alite and belite (3 to 7 µm) are developed on the margins of pores. Radiating needles are developed on the surface of few belite grains. Belite grains are mostly developed as clusters of various shapes and sizes (45 µm to 385 µm). Majority of alite grains are in the size range of 20 µm to 30 µm. Pores of various shapes and sizes (80 to 695 µm) are uniformly distributed in these nodules. Porosity of the clinker is high. The optical micrograph as given in Plate 2 and 3. Plate 2: Formation of belite grains Plate 3: Distribution of alite & belite in CL-C (50x) grains in CL-C (20x) Optical Microscopy of Bulk Clinker, CL-I-B: The clinker phases are moderately developed and in-homogeneously distributed. Majority of alite grains are pseudo hexagonal to hexagonal in shape with broken out line. Other common shapes like triangular, lath and needle shaped alite grains are also developed in the clinker. Numerous inclusions are also present in alite grains. Majority of alite grains are in the size range of 25 µm to 30 µm. Most of belite grains are sub rounded to rounded in shape with corroded margins. Fine globular grains of alite and belite (2 to 6 µm) are developed on the margins of pores. Belite grains are mostly developed as clusters of various shapes and sizes (50 µm to 370 µm). Majority of alite grains are in the size range of 25 µm to 30 µm. Pores of various shapes and sizes (75 to 710 µm)

10 are uniformly distributed in these nodules. Porosity of the clinker is high. The optical micrograph as given in Plate 4 and 5. Plate: 4 & 5: Distribution of alite and belite grains in the lab fired clinker. (10x) The granulometric analysis of both the clinkers are as given under in Table 13. Table 13 Granulometric Analysis of Clinker Phases Quantity Granulometry ( m) Phases (%) Min. Max. Avg. Alite RM-C Belite Alite RM-1 Belite Preparation of Ordinary Portland Cements Ordinary Portland Cement, OPC-C-B and OPC-1-B were prepared by grinding the clinker, CL- C-B and CL-2-B with 5.42 percent gypsum to a fineness of ~300 m 2 /kg and tested for setting time, compressive strength, Le-chatelier and autoclave expansion tests as per Indian Standard Specification IS: and the results are discussed below: Chemical Analysis of Control and Optimised OPC The chemical analysis of OPC-C-B and OPC-1-B were carried out as per Indian Standard Specification, IS: and the results are presented in Table 14. The analysis indicate that in case of OPC-C-B, the cement sample contain percent CaO and percent SiO 2. The SO 3 was found to be 2.33 percent. Similarly in case of OPC-2-B, the analysis indicated that the cement sample contain percent CaO and percent SiO 2. The SO 3 was found to be 2.20 percent. Performance Evaluation of OPC Setting Time The initial and final setting times of Ordinary Portland Cement prepared in laboratory from bulk clinker, CL-C-B and CL-1-B, were determined as per IS: and found to be 150 and 210 minutes for OPC-C-B and 155 and 220 minutes for OPC-1-B respectively. The OPC-C-B and OPC-1-B thus conform to the requirements of IS: for 53 grade OPC with respect to setting time. The results are presented in Table 15.

11 Compressive Strength The compressive strength of Ordinary Portland Cement OPC-C-B and OPC-1-B were determined as per IS: and the results are presented in Table 15. The compressive strengths at 3, 7 and 28 days were found to be 30, 42 and 62 MPa respectively for OPC-C-B and 31, 44 and 64 MPa respectively for OPC-1-B. The Ordinary Portland Cement OPC-.C-B and OPC-1-B thus conformed to the compressive strength development requirements of the Indian Standard Specifications for 53 grade of Ordinary Portland Cements viz. IS: Table 14 Chemical Analysis of Ordinary Portland Cement Sl. No Constituents Determined (%) LOI SiO 2 Fe 2 O 3 Al 2 O 3 CaO MgO SO 3 Na 2 O K 2 O Cl - IR OPC-C-B Cement samples OPC-1-B Soundness Autoclave and Le-chatelier expansion tests on OPC-C-B and OPC-1-B prepared from respective bulk clinkers were carried out as per the procedures laid down in IS: Autoclave expansion was found to be 0.09 percent and Le-chatelier expansion to be 1.0 mm in case of OPC C-B and 0.01 percent and 1.00 mm respectively in case of OPC-1-B. The results indicated high volume stability of both the cement sample i.e. OPC-C-B and OPC-1-B. The performance evaluation of OPC-C-B and OPC-1-B established that the resultant cement from the bulk clinkers CL-C-B and CL-1-B are conforming the various requirements as laid down in Indian Standard specification IS: for 53 grade OPC. Results and Discussions The performance characteristics of control OPC indicated that the cement met the requirement of 53 grade OPC as per IS: The high compressive strength of OPC-1-B is attributed to the development of controlled morphology and grain growth of alite and belite with sharp grain margins. The addition of CAW-C had acted like a catalyst to the clinkersiation leading to good quality of clinker. The presence of CAW-C as raw materials had affected the nuclei formation and resulted in controlled grain growth of alite and belite with improved crystallinity.

12 Table 15 Performance Evaluation of Ordinary Portland Cement OPC-C-B and OPC-1-B Requirement of Property OPC-C-B OPC-1-B IS: (53 Grade OPC) Fineness (M 2 /kg) Not less than 225 Setting Times (Min.) Initial Final Compressive Strength ( MPa) Not less than 30 Not more han Days 7 Days 28 Days Not less than 27 Not less than 37 Not less than 53 Soundness Le-chatelier (mm) Autoclave (%) Not more than 10 Not more than 0.8 Conclusions Based on the detailed and systematic investigations carried out on various alumina wastes samples as generated at the units of M/s Century Metal Recycling, Palwal, the following conclusions were drawn: 1. In case of use as cement raw materials, considering the content of chloride in various alumina wastes, materials namely IDSM-2AL, IDSM-1AL and CP-POD were considered appropriate and mixed in the ratio of 50:25:25 by weight and referred as composite alumina waste, CAW-C and the same were used as cement raw material by replacing alumina bearing additives in raw mix. 2. The results of investigation confirmed that 0.7 percent by weight of CAW-C could be gainfully utilized as raw material replacing alumina bearing additive namely bauxite in present case in the raw mix and good quality clinker could be produced at 1450 o C. 3. The results of the performance evaluation of cement, OPC-1-B prepared from the optimized raw mix RM-1 containing 0.7 percent CAW-C indicated that it surpassed the 3, 7 and 28 day strength limit of 53 grade OPC as per IS:12269 with adequate margins. The high compressive strength of OPC-1-B was attributed to the development of controlled morphology and grain growth of alite and belite with sharp grain margins. The addition of CAW-C had acted like a catalyst during the clinkerisation process. Acknowledgement The authors have freely drawn the information/data from published literature and NCB/ CMR project reports. This paper is being published with the permission of the Director General, National Council for Cement and Building Materials, Ballabgarh, India and Director of Century Metal recycling, Palwal, Haryana, India.