Manufacture of Portland Cement from Claystone of Nfayil Formation Middle Miocene, in Southern Desert of Iraq

The research aims to assess the claystone exposed in the Nfayil Formation (Middle Miocene) for Portland cement (P.C.) manufacturing based on mineralogy and geochemistry. The importance of the study is to avoid the miming of the agricultural soils that are mining now for the cement industry. Claystones of Nfayil Formation and the limestone of the Euphrates Formation were used to design the raw mixture as clay to limestone (1:3). The chemical composition (%) of the designed mixture was calculated using the Alligation Alternative Method (A.A.M.) as CaO (65.52), MgO (1.05), SiO 2 (21.65), Al 2 O 3 (7.43), Fe 2 O 3 (2.62), Na2O3+K2O (1.52) and SO 3 (0.26), which are suitable for P.C. The lime saturation factor (LSF = 92.8), silica saturation factor (SSF = 0.87), alumina ratio (AR = 2.8), silica ratio (SR = 2.16), and calcium to silica (CS = 3.04) of the planned mixture are all within the permissible range. A clinker was successfully manufactured as composed mainly of belite, alite, aluminate, and ferrite.


Introduction
The manufacturing Portland cement (P.C.) is a building material that is utilized all over the world as it is the primary and most common material used in civil engineering structures (Ali et al., 2014).Cement is made in a conventional way by finely pulverizing clinker, which is generated by calcining a combination of argillaceous and calcareous minerals in a wet or dry process (Ali et al. 2014).The main materials using for the P.C. industry are limestone and clay, where the calcium carbonate (CaCO 3 ) is naturally found in calcareous sediments such as limestone, chalky limestone, or marl, while other components (SiO 2 , Al 2 O 3 , and Fe 2 O 3 ) are sourced from clay, iron ore, sand and shale (Newman, and Choo, 2003).Currently, topsoil is utilized as a raw material in the production of P.C., causing reduction of agricultural areas and, eventually, environmental harm (Awadh andAbdullah, 2011 andAwadh andAwad, 2020).According to the concept above, the claystones in the Nfayil Formation (middle Miocene) exposed in the southern desert were considered as an area of interest that can provide the raw material.The Nfayil Formation has 6 m thick of the lower member and 7m thick of the upper member (Sissakian, 1997;and Awadh, and Al-Ankaz, 2016) encouraging it to be a source of clay for the industry of P.C.The study area covers of about 30 km 2 is located to the north of AL-Absaiya within the Al-Muthana governorate (Fig. 1) with coordinates listed in Table 1.The aim of the current research is to assess the claystone of the Nfayile Formation for the P.C. industry.

Geological Setting
The exposed formations in the study area are Ghar and Nfayil formations (Early Miocene to Middle Miocene respectively) which are composed of sedimentary rocks (Fig. 2).The Euphrates, Nfayil, Injana and Dibdibba formations cropping out in the zone of Abu jir fault, is good evidence for interpreting the fault activity (Al-Dabbas et al., 2013;Awadh, 2014;Awadh and Muslim, 2014;Awadh el.al. Awadh, 2018;Al-Dabbas et al., 2019;Awadh and Al-Owaidi, 2020).The Nfayil Formation is divided into two members (lower and upper) The lower member includes three depositional cycles exposed in the study area.Cycle-1, the lowest one, it is consisted of 3.2 m claystone with the color of brown to yellowish-brown, medium tough to soft, obscured contact, conchoidally fractured, with rusty patches.Sandstone (0.4m) is overlain claystone with a color of yellow, medium tough, sharp contact, thickly bedded.Cycle-2 is emplaced on cycle-1 consisting of 0.1 m of green marl, medium tough to soft, sharp contact.Pink marly limestone, medium tough, sharp contact, with Oyster and yellow patches.The thickness of this bed is 0.3 m.Light yellow marly limestone, medium tough, gradational contact, with Oyster.The thickness of this bed is 0.5m.Fossiliferous limestone of 0.1m characterized by yellowish-white, tough, sharp contact, thinly bedded.Yellowish white marly limestone (0.4m) of medium tough and sharp contact has a few fossils.Yellowish white, limestone (0.3m), tough, gradational contact, with molds of fossils.Cycle-3 is emplaced on cycle-2, consisting of green marl (1.0m), medium tough to soft, sharp contact overlain marly limestone (1.2m) with a color of grayish white, medium tough, sharp contact.Fossiliferous limestone (0.5m), yellowish-white color, tough, sharp contact, medium bedded.In the study area, the total thickness of the lower member of the Nfayil Formation is 8.0 m (Zaini et al., 2014) (Fig. 3).The upper member includes two depositional cycles exposed in the study area.Cycle-1 is exposed to the east, northeast, and north of the study area.It consisted of 3.5 m brown claystone, medium tough to soft, obscured contact, conchoidally fractured, with rusty patches.Calcareous sandstone (0.3m) overlies claystone with a color of pinkish-white, medium tough, sharp contact.Cycle-2 is emplaced on cycle-1, it exposed the north and east sides of the research area.It is consisting of whitish-gray sandstone (2.7 m), medium tough to friable, obscured contact, medium grains containing pebbles and fragments of carbonate rocks.Whitish gray sandy limestone (1.8 m), overlie of sandstone, tough to medium tough, sharp contact, medium to thinly bedded, coarse to medium grains of sand, contain fossils (Fig. 3).

Materials and Methods
Sixteen samples of claystones were collected from 16 sections in the Nfayil Formation by using a channel method.These samples were analyzed for CaO, SiO 2 , Al2O 3 , Fe 2 O 3 , MgO, K 2 O, Na 2 O, P 2 O 5 , TiO 2 , Cl -, MnO, L.O.I and SO 3 by using X-ray fluorescence (XRF) at the laboratory of the Environmental and Water Directorate Environmental Research Center.The STG2 was used as reference material for standardized XRF.Finally, one representative was chosen to be a raw material in the production of clinker.Limestone was acquired from an exposed quarry within the Euphrates Formation outside of the research area to produce a cement mixture.Clinker manufacturing was carried out at the labs of the Ministry of Construction and Housing (Building Research Center).The P.C. is made by mixing its constituents (claystone and limestone) to get the required chemical composition, to make them more reactive, these materials were crushed into small particles and passed through a sieve of 75 microns before being thoroughly mixed together.The clinker was analyzed using XRD device, type D2 phaser, Lab X 6000 XRD diffractometer with the following parameters, a target of Cu kα 2.7kw tube, current: 80 ma, speed 1cm/min, power: 60 kV, filter Ni which was conducted in the laboratory of the Ministry of Science and Technology, Department of Materials Science.The 2Ө scan of the bulk samples was 5 -60° to cover all clinker phase beaks.

Raw Material Blending Process
The typical raw mix for the kiln feed is presented in Table 3.The chemistry of the raw meal entering the kiln must be closely regulated for successful raw-mix production in cement manufacture for effective raw-mix preparation in cement manufacturing (Bond et al., 2000).The clinker production process's main chemistry is determined by the kiln feed raw mix.The range of chemical oxides for produced P.C. by using the A.A.M. (Kohlhaas, 1983 andDuda, 1985).According to A.A.M., the concentration of raw materials mixture (claystone and limestone) is determined depending on the CaO content.The needed lime content is established as a set point (S.P.) because its value falls below the acceptable percentage, extra lime must be added to bring the ratio up to the required specification limits using additive limestone from another location (Al-Auweidy, 2013).The fraction of limestone to claystone in a kiln feed is used to calculate the number of oxides free of L.O.I. (Awadh and Awad, 2020).Fig. 7 shows how to calculate the raw mix designer.

Kiln Feed Parameters
The raw mix design is calculated using the compositional characteristics of the clinker.The level translation of silica, alumina, and iron oxide to their most basic calcium compounds is measured by L.S.F. in clinker parameters (Bhatty et al., 2011).According to Duda (1985), the L.S.F.varies from 90-95 %, while according to Chatterjee (2009), the L.S.F.ranges from 90 to 97%.According to Newman and Choo (2003), the correct L.S.F.ratio is within the range of 95 and 98%.According to Iraq's Quality Standard Number 5, L.S.F. is 90-100 % (I.Q.S, 1984).A high L.S.F.needs a significant thermal expenditure for clinker burning within the kiln; as a result, the cement has more strength, but it also requires more fuel, resulting in a higher product price and damage to the kiln lining.If L.S.F. is less than 92, extra free lime (CaO) will develop in the cement.When concrete with a high free lime cement is used in gypsum soil, the CaO soluble in water reacts with the gypsum to create Ettringite with 26 molecules of H2O, causing the concrete to slowly deteriorate (Al-Mufty, 1997) according to the equation.
3CaO+3CaSO 4 +Al 2 O 3 +26H 2 O→Ca 6 (Al (OH) 6 )2(SO 4 )3.26H 2 O S.S.F. the combining efficiency of silica with lime left after forming C3A and C4AF, according to Kebede, 2010, the value estimated between 0.85 and 0.95 can give perfect cement.Hydraulic modulus (H.M.) is expressed by the optimal lime concentration, which varies from 1.7-2.3,but the high-quality is 2 (Ghosh, 2002).The ratio of silica (S) to the sum of aluminum (A) and iron (F) oxides is measured as S.R. (Peray, 1986 andBhatty et al., 2011).The range of (S.R.) for the cement clinker is1.8 -3.2 (Knofel et al., 1984), but the best value according to Gouda (1979), Kohlhaas, (1983) and Duda, (1985) is 2.2 -2.6.A.R. is a measurement of the ratio of aluminum oxide (A) to iron (F) oxide.C.S. refers to the calcium to silica ratio (Almeida, 2010), usually in cement manufacturing, the C.S. should be not less than 2 (Kebede, 2010).The clinker parameters were calculated from the following equations: The kiln feed parameters were determined and listed for the raw material adjustment in Table .5.All of the clinker parameter results are within the acceptable ranges for clinker product success.

Clinker Manufacturing
The raw materials weighed 160 g and were made up of claystone (51.52 g) and limestone (108.48 g), contributing 32.2 % and 67.8%, respectively.According to the A.A.M. technique, this mixture was combusted to 1450°C in an electrical furnace.The raw ingredients and clinker sample show in Fig. 8 (A ) and (B).This research found the clinker sample weight after combustion is 137g.The release of volatiles (SO 3 , molecular water, Cl, CO 2 , and alkalis) is caused by the loss of clinker weight.The clinker produced contains mineral phases such as belite, alite, ferrite, aluminate, and calcium oxide (Fig. 9).

Conclusions
Mineral components aided the source of oxides used for the cement raw materials.The average (%) of chemical constituents of claystone from the Nfayil Formation is CaO (8.64), MgO (2.7), SiO 2 (47.83),Al 2 O 3 (16.37),Fe 2 O 3 (6.05),Na 2 O 3 (1.57)K 2 O (1.52), and SO 3 (0.2).The claystone was within the normal range for cement raw materials and looks to be qualified for use in cement manufacturing (Duda 1985).The chemical nature of the claystone beds shows that they include suitable raw materials that must be mixed with limestone at a 3:1 ratio to create effective raw materials that meet the standard.Also, several cement conditions must be balanced for the raw materials of cement.The parameter values of the samples analyzed in the components of the raw materials L.S.F.(92.8 %), S.S.F.(0.87 %), S.R. (2.16%), AR (2.8%), H.M. (2.08%) and C.S. (3.04%) are sufficient for the appropriate requirements for clinker processing.The claystone layer's kiln feed parameters are within the required limits.

Fig. 1 .
Fig.1.Location map of the study area

Fig. 2 .
Fig. 2.Geological map of the study area shows the location of the Sampling site(after Zaini, et al, 2014)

Fig. 3 .
Fig. 3. Stratigraphic column of Nfayil Formation in the study area

Fig. 5 .
Fig. 5.X-ray diffractograms of sample S8-ch (claystone); Bulk sample, B) various treatments on the directed clay fraction The free L.O.I. percentages of all oxides in the raw mix are shown in(Table.4).

Table 1 .
Coordinates of the study area

Table 3 .
Oxides values of typical raw mix material.

Table . 5
. Results of kiln feed calculations based on clinker parameter equations