Claims:We Claim:
1. A process for manufacture of calcium aluminate cement (CAC) from secondary steelmaking by products comprising:
involving (a) Ladle Slag generated during secondary steelmaking process 50 - 70% by wt free of any limestone based CaO sources and (b) alumina source 30-60% by wt.;
maintaining the particle size of the ingredients less than 100 mesh size;
sintering at temperatures between 1400 °C and 1500 °C for a time of 2 h and 4 h followed by natural cooling to room temperature inside the furnace; and
obtaining calcium aluminate cement (CAC) therefrom.
2. A process as claimed in claim 1 comprising obtaining the cement prepared from clinker after grinding to a fineness less than 90 µm size suitable for use as a hydraulic binder for refractory and construction applications.
3. A process as claimed in anyone of claims 1 or 2 comprising the steps of:
e. grinding and screening the ingredients to achieve desired size fraction;
f. preparing a mixture from the said ingredients;
g. heating said mixture to form a clinker;
h. powdering said clinker to form the aluminous cement.
4. A process as claimed in anyone of claim 1 to 3 wherein said ladle slag is provided as the 100% source of CaO and partial source of Al2O3 in the clinker.
5. A process as claimed in anyone of claim 1 to 4 wherein said Alumina source comprises Indian or Chinese Bauxite, Calcined Alumina, Tabular Alumina or mixtures thereof.
6. A process as claimed in anyone of claim 1 to 5 wherein clinker is prepared by dry mixing the ingredients and heating the clinker mix in a muffle furnace.
7. A process as claimed in anyone of claim 1 to 6 wherein CO2 emission due to dissociation of limestone during clinker making process is completely eliminatedso that emission of “Greenhouse Gas” (CO2) during clinker making is reduced by 60%.
8. Clinker composition comprising of steelmaking slag, preferably ladle slag after secondary refining process by Al-killing 50 - 70% by wt and an Alumina source 30-60% by wt,
9. Clinker as claimed in claim 8 providing for calcium aluminate cement having an initial setting time of about 22-425 min, final setting time of 57-600 min, cold crushing strength of 150-350 kg/cm2 after 24 h of water addition.
10. The calcium aluminate cement as claimed in claim 9 which has an Al2O3 content of at least 50%.
11. The calcium aluminate cement as claimed in anyone of claims 8 to 10 comprisingAl2O3: 40 to 65%preferably >50%, CaO: 22 to 40% preferably < 36%, SiO2: 2.5 to 8% preferably < 5%, Fe2O3: 1 to 5% preferably <3.0%, MgO: 3 to 7% preferably <4%.

Dated this the 12th day of October, 2018
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION
The present invention relates to a process for manufacturing of hydraulically boundcalcium aluminate cement (CAC) clinker from by-product of secondary steelmaking processandcalciumaluminate cement (CAC) obtained thereof from process waste, having a minimum Al2O3 content of 50% by weight. More particularly, the present invention is directed to provide a low cost cement clinker using selective mix of process wastes comprising Ladle Slag generated during secondary steelmaking process 50 - 70% by wt and alumina source 30-60% by wt, wherein the Ladle slag was used as the 100% source of CaO by replacing limestone and partial source of Al2O3 in the cement, thereby reducing the CO2 emission by 60%. The process requires maintaining the particle size of the ingredients less than 100 mesh size and sintering at temperatures between 1400 °C and 1500 °C for a time of 2 h to 4 h, followed by natural cooling to room temperature inside the furnace. The cement prepared from the clinker after grinding to a fineness less than 90 µm size can be used as a hydraulic binder for refractory and construction applications.
BACKGROUND OF THE INVENTION
Calcium aluminate cements (CACs), also known as high alumina cements, have an Al2O3 content of 40-80 wt%, the main compound being C12A7, CA, CA2. The CAC is classified into low, medium and high purity based on their Al2O3 content and fast, moderate and slow based on setting time.
Though calcium aluminate cements are similar to Portland cements as both require water for hydration and strength development, the basic difference between them is Portland cements are manufactured by reacting limestone and clay to produce calcium silicates, whereas calcium aluminate cements are manufactured from a mixture of limestone and bauxite or other suitable materials containing more than 50% Al2O3. In addition, calcium aluminate cement develops strength within 24h of mixing with water as compared to that developed in 28 days for Portland cement. The manufacturing process generally comprises of clinker formation by heating (sintering, melting) the mixture in an electric furnace, open-hearth furnace or rotary kiln and subsequently grinding the clinker to obtain calcium aluminate cement.
The clinker making process from limestone (CaCO3) involves release of carbon dioxide (CO2) due to its conversion into calcium oxide (CaO) during heating, thereby effecting the environment. Another disadvantage being consumption of substantial amount of natural resources. Recent statistic report shows 4.1 billion metric tons of cement production worldwide in the year 2017 and is expected to be around 4.8 billion metric tons by 2030.(https://www.statista.com/statistics/ 267364/world-cement-production-by-country/).
Cement manufacturing is an energy intensive process with substantial CO2 emission. As reported in 2011/278/EU, the CO2 emission is approximately 0.766 kg per tonne of cement clinker with a total emission recorded to be 573 million tonnes in 2011. Similarly, the energy required to produce 1 tonne clinker is 3.6 GJ through a modern dry process (GNR Project reporting, 2012) and 5.7 GJ for a wet process (Taylor, 1997). Coal continues to be the main fuel for cement industry and is used up to as high as 80% of the total fuel used. During clinker making process, the CO2 is evolved from two sources, viz. combustion emission related to the combustion of fuels for energy production accounting for approximately 40% of total emission and process emission related to the calcination of limestone that accounts for 60%.
To strengthen its environmental position, the cement industry is facing new challenges to reduce the CO2 emissions. This has called for a need in improving the clinker recipeand manufacturing method by utilizing materials that require less energy and thusmaking the process both economical and eco-friendly.
Iron and Steelmaking slags, by-product of metal extraction process, generally consist of inorganic oxides (silica, calcia, alumina, magnesia and/or iron oxides). They are considered as suitable raw materials for cement making owing to their hydraulic nature. The mineral fractions present in the steelmaking slags are primarily alite (3CaO.SiO2, C3S), belite (2CaO.SiO2, C2S), celite (3CaO.Al2O3, C3A), brownmillerite (4CaO.Al2O3.Fe2O3, C4AF) which help in achieving the binding property of the slag when mixed with water. A fair amount of work has already been carried out on use of the waste slag generated in iron and steel making process in cement and cement mixes. Some prior works in the related field are summarized below:
US Patent No. 4,071,373A dated 31st Jan 1978 (Aluminum Alloy Refiners Association) by Keiichi Akiyama describes a process for the manufacture of aluminous cement from a mixture of predetermined amounts of aluminum smelting residue, limestone, aluminum siliceous clay, and, if necessary, fluorite and manganese ore for the acceleration of oxidation. The mixture is finely crushed and then burnt at temperatures between 1300°C and 1500°C to form a clinker which is then powdered to produce an aluminous cement. The product contains no harmful chemical compositions that tend to become a source of public hazards such as air or water pollution.
US Patent No. 5,516,357A dated 14th May 1996 (Holcim Ltd.) by Alfred Edlinger and Theo Rey describes a process for preparation of a cement from metallurgical slags, in which liquid slags from blast furnace (30 to 80% by weight) and converter (20 to 70% by weight) are mixed together, with lime addition if required, followed by controlled cooling above 1000°C, preferably above 1200°C to achieve the alite, belite and bredigite phases during cooling required for the hydraulic properties. The solidified product obtained is subsequently granulated and/or ground in order to obtain directly cement with improved hydraulic properties, in particular increased final strength.
US Patent No. 6,491,751 dated 10th Dec 2002 (Texas Industries, Inc.) by Robert C. Watson describes a method for manufacturing cement from a mixture of finely ground primary steelmaking slag (BOF slag) and other raw materials. The fine dry mixture, cold or preheated, was heated in a kiln to produce the clinker.
US Patent No.2,007,000,677,8A1 dated 11th Jan 2007 by Alexander Kehrmann describes a method of producing a cement clinker from a mixture of calcium oxide, silicon dioxide, aluminium oxide and iron oxide by means of mixing, grinding and burning. According to the invention, the mixture of raw materials consists of a calcareous component and converter slag, the converter slag being added in a proportion of up to 30% by weight. Natural resources of raw materials can hereby be preserved and the carbon dioxide output during burning of the cement clinker can be reduced.
US Patent No. 8,038,791,B2 dated 18th Nov 2011 (Levy Edward Co) by Ronald R. Piniecki describes a system and method of manufacturing a cement clinker from a mixture of feedstock material and a ladle metallurgical facility slag material derived from a ladle metallurgical facility steel production system with composition having CaO> 45%, Al2O3> 3% and Fe2O3< 12%. The feedstock material comprised one or more raw materials, such as, limestone, clay and sand whereas the ladle slag was used up to 12% as the starting materials. The raw materials were fired in a rotary kiln to produce clinker.
Patent No. PCT/KR2013/006680 dated 25th Jul 2013 (Research Institute of Industrial Science and Technology, Korea) by Jung Young-su and Kim Hyung-suk relates to an Alumina cement using 2 to 50 wt% molten blast furnace slag, 1 to 5 wt% liquid ladle slag, 27 wt% or less of limestone and 45 to 80 wt% of bauxite prepared by fusion in an electric furnace followed by cooling. According to the invention, the molten blast furnace slag and the high-temperature ladle slag are used as alternatives to raw materials for alumina cement, thereby reducing the use of expensive raw materials and enabling manufacturing costs to be saved through the decrease in use of electrical energy resulting from the use of the sensible heat from the material.
The crux of the present invention, in particular, differs from the prior art by way of developing a process for producing a calcium aluminate clinker by utilizing the process waste (ladle slag, hereafter referred as LHF slag) as a source of CaO and Al2O3,thus replacing thelimestone completely and bauxite partially. The CO2 emission due to dissociation of limestone during clinker making process is therebycompletely eliminated and the natural occurrences of raw materials are preserved. Recycling of process waste lowers down the manufacturing cost as well.
In connection with the present invention, reference has been made to the Japan Industrial Standard R2511 for "The aluminous cement for refractory materials" which mentions minimum Al2O3 content in the second class of such cement is 35% whereas the Fe2O3 content is below 10% and CaO is below 40%.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to provide a process for manufacturing a calcium aluminate cement (CAC) using steel making process waste for clinker making involving raw material input comprising a mixture of Ladle slag of Al-killed steel in the range of 50 to 70 wt %and 30 to 60 wt% of Alumina source and the calcium aluminate cement (CAC) product obtained thereof.
A further object of the present invention is directed to provide a calcium-aluminate cement using steel making process waste to obtain an Al2O3 content of minimum 50% in the cement.
A still further object of the present invention is directed to provide a calciumaluminate cement using steel making process waste as a replacement of limestone and bauxite natural raw materials for clinker making, thereby reducing the manufacturing cost.
A still further object of the present invention is directed to provide a calciumaluminate cement using as much steel making process waste as possible having large content of CaO to replace the limestone completely and reducing the CO2 emission by 60% due to dissociation of limestone during clinker making process.
A still further object of the present invention is directed to a process for producing calcium aluminate cement wherein preferably LHF slag is used in the range of 50-70%as total replacement of limestone and partial replacement of Al2O3 raw material source, in combination withthe Al2O3 source content preferably in the range of 30 to 60% by weightto achieve the composition required for the CAC.
A still further object of the present invention is directed to a process for producing calcium aluminate cement wherein LHF slag is used as a pre-melted material having a melting temperature of less than 1400°C, therefore will require less energy for sintering compared to natural raw materials.
Another object of the present invention is directed to provide a calcium-aluminate cement using steel making process waste which can be used for refractory or construction applications as a hydraulic binder.
Yet another object of the present invention is directed to provide a calciumaluminate cement using steel making process waste in order to recycle and utilize steel plant by-products, so as to close the sustainable production loop.
A further object of the present invention is directed to provide a calcium aluminate cement using steel making process waste where the mix comprising selective proportion of process waste (LHF slag: 50-70 wt%) and Al2O3 source (30-60 wt%), the method comprising grinding the mixture to less than 100 mesh size, sintering of the mixture in a muffle furnace to form a Calcium Aluminate clinker and allowing the clinker to cool naturally in the furnace. Since the LHF slag contains SiO2 and Fe2O3 as its constituents, it is unnecessary to add SiO2 and Fe2O3 on purpose.
A still further object of the present invention is directed to provide a calcium aluminate cement using steel making process waste, wherein the clinker is ground to cement fineness of less than 90 µm size and hydraulically set and dried cement articles meet the property requirements e.g. initial and final setting times, cold crushing strength after 24 h to suit the intended applications.
SUMMARY OF THE INVENTION:
The basic aspect of the present invention is directed to a process for manufacture of calcium aluminate cement (CAC) from secondary steelmaking by products comprising:
involving (a) Ladle Slag generated during secondary steelmaking process 50 - 70% by wt free of any limestone based CaO sources and (b) alumina source 30-60% by wt.;
maintaining the particle size of the ingredients less than 100 mesh size;
sintering at temperatures between 1400 °C and 1500 °C for a time of 2 h and 4 h followed by natural cooling to room temperature inside the furnace; and
obtaining calcium aluminate cement (CAC) therefrom.
A further aspect of the present invention is directed to said process comprising obtaining the cement prepared from clinker after grinding to a fineness less than 90 µm size suitable for use as a hydraulic binder for refractory and construction applications.
A still further aspect of the present invention is directed to said process comprising the steps of:
a. grinding and screening the ingredients to achieve desired size fraction;
b. preparing a mixture from the said ingredients;
c. heating said mixture to form a clinker;
d. powdering said clinker to form the aluminous cement.
Another aspect of the present invention is directed to said process wherein said ladle slag is provided as the 100% source of CaO and partial source of Al2O3 in the clinker.
Yet another aspect of the present invention is directed to said process wherein said Alumina source comprises Indian or Chinese Bauxite, Calcined Alumina, Tabular Alumina or mixtures thereof.
A further aspect of the present invention is directed to said process wherein clinker is prepared by dry mixing the ingredients and heating the clinker mix in a muffle furnace.
A still further aspect of the present invention is directed to a process wherein CO2 emission due to dissociation of limestone during clinker making process is completely eliminated so that emission of “Greenhouse Gas” (CO2) during clinker making is reduced by 60%.
A still further aspect of the present invention is directed to a Clinker composition comprising of steelmaking slag, preferably ladle slag after secondary refining process by Al-killing 50 - 70% by wt and an Alumina source 30-60% by wt,
A still further aspect of the present invention is directed to said Clinker providing for calcium aluminate cement having an initial setting time of about 22-425 min, final setting time of 57-600 min, cold crushing strength of 150-350 kg/cm2 after 24 h of water addition.
Another aspect of the present invention is directed to saidcalcium aluminate cement which has an Al2O3 content of at least 50%.
Yet another aspect of the present invention is directed to said calcium aluminate cement comprisingAl2O3: 40to 65% preferably >50%, CaO: 22 to 40% preferably < 36%, SiO2: 2.5 to 8% preferably < 5%, Fe2O3: 1 to 5% preferably <3.0%, MgO: 3to7% preferably <4%.

A further aspect of the present invention is directed to said process to provide a calcium aluminate cementwhich is settable hydraulically by addition of water.

A still further aspect of the present invention is directed to said process to produce a calcium aluminate cement clinker wherein the ladle slag is used as the 100% source of CaO and partial source of Al2O3 in the cement clinker, thereby preserving the natural resources and reducing the manufacturing cost.

Another aspect of the present invention is directed to said process to produce a calcium aluminate cement wherein ladle slag becoming powdered during cooling is considered as the clinker ingredient to minimize manufacturing cost.

Importantly, in said process to produce a calcium aluminate cement, the mixture of ladle slag and alumina source of pre-determined proportion is heated in a muffle furnace at temperatures between 1400 oC and 1500 oC for a time of 2 h to 4 h to obtain the clinker.

Another aspect of the present invention is directed to said process to produce a calcium aluminate cement wherein the clinker is cooled to room temperature and ground to a size of less than 90 µm fineness to obtain cement.
In the process according to the invention when the slag content is more than 50% by weight, can replace the limestone completely and reduce raw material costs. However, if the content of the slag exceeds 70% by weight, it is difficult to achieve the composition required for the CAC. Further, the LHF slag alone is difficult to meet the Al2O3 requirement for developed CAC. Accordingly, the present invention preferably used LHF slag as partial replacement of Al2O3 raw material source. The Al2O3 source content is preferred in the range of 30 to 60% by weight, as for less than 30% by weight, it is difficult to provide the required Al2O3 content in the cement and for more than 60% by weight, reduction in manufacturing cost is lowered.
To further reduce the cost of manufacturing, LHF slag in powder form is preferred. The LHF slag gets powdered and forms dust during natural cooling in the slag yard. The clinker making process usually requires temperatures between 1400°C and 1500°Cby sintering route. The present invention therefore uses LHF slag, which is a pre-melted material and has a melting temperature of less than 1400°C, therefore will require less energy for sintering compared to natural raw materials.
The above and other objects and advantages of the present invention are described hereunder with reference to accompanying figures and examples.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Fig. 1: Process flow of cement preparation as per the invention.
Fig. 2: shows graphically the Particle size distribution of clinker ingredients.
Fig. 3: show the images of clinker blocks for different LHF Slag:Al2O3 ratio sintered at 1400°C for 2h.
Fig. 4: Micrograph showing various hydrated phases formed in cement paste.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES

The present invention relates to a process for manufacturing of hydraulically bound calcium aluminate cement (CAC) clinker from byproduct of secondary steelmaking and calciumaluminate cement (CAC) obtained thereof from process waste, having a minimum Al2O3 content of 50% by weight. More particularly, the present invention is directed to provide a low cost cement clinker using selective mix of process wastes comprising Ladle Slag generated during secondary steelmaking process 50 - 70% by wt and alumina source 30-60% by wt, wherein the Ladle slag was used as the 100% source of CaO by replacing limestone and partial source of Al2O3 in the cement, thereby reducing the CO2 emission by 60%.

Referring to Fig. 1, a method 100 for manufacturing clinker from steel making slag, is shown at steps S.101-S.111. At step S.101, a LHF slag is obtained from steel ladles of a steel production system after secondary steelmaking process. Grinding and screening of the slag is done through steps S.102 and S.103. Since the LHF slag gets powdered during cooling, step S.102 may be avoided if necessary. Steps S.104 to S.106 describe the material preparation for Al2O3 source. The proportion of LHF slag and Al2O3 source that will compose the ingredients of the clinker recipe is determined in the step S.107. Step S.108 ensures homogeneous mixing of the clinker ingredients. In step S.109, the mixture of ingredients is heated in a muffle furnace to obtain clinker and cooled in furnace to room temperature in step S.110 which is subsequently ground in step S.111 to obtain cement of desired fineness after cooling.

Fig. 2 shows the particle size distribution of the clinker ingredients confirming 100% of the material having a particle size less than 100 mesh size (150 µm).

Fig. 3 shows photographs of clinker produced according to the invention for few batches after heating at 1400 oC for 2 h. The difference in colour of the sinter is attributed to the LHF slag content in the clinker. Higher the slag content, darker is the colour of the clinker.
The strength of a cement paste is governed by the hydrated phases formed by reacting with water. Fig. 4 illustrates the microstructure of cement paste as per one embodiment showing presence of C3AH6 and hexagonal plates of C2AH8. The strong and very dense close structure with well-developed flakes of C3AH6 and C2AH8 are responsible for high early strength of the cement.Formation of flaky-plate like Gehlenite hydrate (C2ASH8) and calcium silicate hydrate (CSH) fibers help in achieving the 24 h strength in the cement paste.
The invention will now be illustrated by means of the following examples. However, the following examples are only for explaining the present invention in more detail, but scope of the present inventionis not limited to theparticular embodiments only.
The raw materials used were fine-grained LHF slag as a source of CaOand calcined alumina, Indian and/or Chinese bauxite, tabular alumina as a source of remaining Al2O3 in the clinker having the chemical composition shown in Table 1.
The water demand for achieving the standard stiffness, the setting times and the compressive strength on paste was determined after 24 h for all compositions.
Table 1: Chemical composition of the raw materials
Material CaO (wt. %) Al2O3(wt.%) SiO2 (wt.%) Fe2O3(wt.%) MgO (wt.%)
LHF Slag Type A 42-50 10-16 18-26 1-3 12-18
Type B 45-55 22-36 2-7 1-5 4-9
Al2O3 Source Calcined Al2O3 98-99 < 0.05 < 0.05
Indian Bauxite < 0.5 80-85 < 3.0 5-8 < 0.5
Chinese Bauxite < 0.5 84-86 5-6 1-2 < 0.5
Tabular Al2O3 > 99.0 <0.05 <0.1

Example 1:A cement clinker comprising of 60% by weight of LHF slag, 40% by weight of Alumina and having a particle size not more than 100 mesh.
A method for the preparation of the clinker, comprising the steps of homogeneous mixing of the raw materials in dry condition, sintering of the mix at 1400°C for 4 h followed by natural cooling inside the furnace to room temperature.

A method for the preparation of cement paste, comprising the steps of grinding the clinker to less than 90 µm size, addition of 37% water and casting into blocks. The chemical indicators:CaO: 30-32%, Al2O3:56-58%, SiO2:3-4%, Fe2O3:1-2% and physical indicators: initial setting time 160-190 min, final setting time 290-320 min, compressive strength (24h) 280-350 kg/cm2.

Example 2: A cement clinker comprising of 55% by weight of LHF slag, 45% by weight of Alumina and having a particle size not more than 100 mesh.
A method for the preparation of the clinker, comprising the steps of homogeneous mixing of the raw materials in dry condition, sintering of the mix at 1500°C for 2 h followed by natural cooling inside the furnace to room temperature.

A method for the preparation of cement paste, comprising the steps of grinding the clinker to less than 90 µm size, addition of 30-32% water and casting into blocks. The chemical indicators: CaO:25-28%, Al2O3:60-62%, SiO2:3-4%, Fe2O3:1.5-2% and physical indicators: initial setting time 190-205 min, final setting time 445-455 min, compressive strength (24h) 210-250 kg/cm2.

Example 3: A cement clinker comprising of 50% by weight of LHF slag, 50% by weight of Alumina and having a particle size not more than 100 mesh.
A method for the preparation of the clinker, comprising the steps of homogeneous mixing of the raw materials in dry condition, sintering of the mix at 1400°C for 4 h followed by natural cooling inside the furnace to room temperature.

A method for the preparation of cement paste, comprising the steps of grinding the clinker to less than 90 µm size, addition of 32-33% water and casting into blocks. The chemical indicators: CaO:25-27%, Al2O3:62-65%, SiO2:3-4%, Fe2O3:1.5-2.0% and physical indicators: initial setting time 240-260 min, final setting time 400-425 min, compressive strength (24h) 180-210 kg/cm2.

Example 4: A cement clinker comprising of 65% by weight of LHF slag, 35% by weight of Alumina and having a particle size not more than 100 mesh.
A method for the preparation of the clinker, comprising the steps of homogeneous mixing of the raw materials in dry condition, sintering of the mix at 1400°C for 4 h followed by natural cooling inside the furnace to room temperature.

A method for the preparation of cement paste, comprising the steps of grinding the clinker to less than 90 µm size, addition of 38.5-39.5% water and casting into blocks. The chemical indicators: CaO:32-34%, Al2O3:52-55%, SiO2:3.5-4.5%, Fe2O3:2-3% and physical indicators: initial setting time 20-45 min, final setting time 50-75 min, compressive strength (24h) 170-225 kg/cm2.

Setting time and compressive strength of the cement paste depend on the various calcium-aluminate phases present and their ability to form different hydrates upon reacting with the water. It would be evident from the above results that the cement compositions of the invention have substantial strength for refractory applications.

Typical properties of the developed cement are shown in Table 2. Properties of a calcium aluminate cement commercially available(source M/s PKV Refractories), in India is provided for comparison. Accompanying Figures 2-4 shows (a) particle size analysis of starting material for clinker, (b) Clinker blocks for different slag:Al2O3 ratio sintered at 1400°C for 2h, (c) micrograph of cement paste showing different hydrated phases formed after 24h of hydration.

Table 2: Typical properties of developed cement
Parameter Commercial Cement Developed Cement
Water required (%) 36 37
Initial setting time (min) 170 175
Final setting time (min) 298 305
CCS (kg/cm2) after 24 h 210 310

As described above, the present invention has advantages in that the LHF slag, which has up till now very limited application or disposed of as waste, can be recycled and the calcium aluminate cement product manufactured therefrom by the present invention can be utilized in the fields of construction and refractory applications.It is thus possible by way of the present invention to provide calcium aluminate cements using appropriate proportion of process waste comprising 50-70% by wt LHF slag as 100% replacement of limestone and partial replacement of bauxite, thereby reducing the CO2 emission by 60% during clinker making process.