Chemical analysis of some Portland cement commonly used in Nigeria was carried out. All the cement studies were found to be good for concrete work especially where no special property is required. The concentration levels of heavy metals in all the cement samples were above the tolerance limit and therefore need to be regulated

Birnin-Yauri, UA

Ibrahim, HH

Muhammad, C

Umar, A

English

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Available online at http://www.ajol.info/index.php/njbas/index  Nigerian Journal of Basic and Applied Science (June, 2012), 20(2): 182-184   ISSN 0794-5698  Assessment of Pollution Potentialities of some Portland Cement  1H.H. Ibrahim; *1U.A. Birnin-Yauri, 1C. Muhammad and 2A. Umar 1Department of Pure and Applied Chemistry, Usmanu Danfodiyo University, Sokoto, Nigeria 2Department of Chemistry, University of Abuja, Abuja, Nigeria [*Corresponding Author, E-Mail: uabyauri@yahoo.com; : +234(0)8038099456] 182  ABSTRACT: Chemical analysis of some Portland cement commonly used in Nigeria was carried out. All the cement studies were found to be good for concrete work especially where no special property is required. The concentration levels of heavy metals in all the cement samples were above the tolerance limit and therefore need to be regulated. Keywords: Portland cement, Heavy Metals,  X-ray Analysis, Pollution, Sokoto   INTRODUCTION Trace metals are naturally present in the biological world in acceptable quantities, but increase of these metals through an anthropogenic contribution has since the last century been known to harmed humans and environment (Archi et. al., 2011). Environmental safety and management has always being strategic issue of discussion in every society that is striving to attain or has attained industrialization since industrialization is synonymous with environmental pollution.  Cement industry has been in operation in Nigeria for many decades and has contributed to Nigerian Economy greatly (Taylor, 2009). Despite the remarkable achievements recorded in the use of cement, it studies have shown that it is associated with some environmental problems such as emission of air  pollutants in form of dust, gases, noise and vibration during the process of manufacture (Oleru, 1984). Cement is also associated with heavy metals as evident in many studies conducted (Ahmed et al., 2009). Heavy metals are known to pose serious health problems to humans, affect plant growth and general damage to ecosystem (Bagudo et al., 2008; Peter et al., 2009).  The aim of this work is to assess the suitability of the selected cement for concrete work and to determine the levels of heavy metals in the cement samples for it potential harmfulness on human and environment.  MATERIAL AND METHOD Sample collection Different cement samples namely Ashaka, Burham, Dangote, Wapco were bought from Wuse Market in Abuja while Sokoto Cement was bought from Sokoto Market. 50g of each sample was taken in clean labelled polythene bag as soon as the cement bag was opened to avoid surface contamination and kept for further analysis.  Apparatus and reagents  Determination of heavy metals was done using Atomic absorption spectrophotometer (AAS) (Perkin – Elm 4000 model) at suitable wavelength for each metal. Cement chemical composition was done using XRF analyzer. All reagents used were of analytical grade.  Digestion of Sample  Cement sample (1g of each) was placed in a 1000 cm3 micro Kjeldahl flask previously washed with nitric acid and distilled water. 10cm3 of concentrated nitric acid was added, 1cm3 of perchloric acid and then 2cm3 of concentrated sulphuric acid. The mixture was swirled gently and slowly and then heated on digester in a fume cupboard. The mixture was then cooled, filtered as diluted into 100cm3 volumetric flask to the mark. All Samples were treated in same manner  Determination of Free Lime 20cm3 of ethylene glycol were placed in Erlenmeyer flask stopped and heated in a water bath at 700C.Then 0.5g of samples was transferred into the flask covered and shaken for 15 minutes and then filtered by vacuum filtration. 30cm3 of 0.1M HCl was added to the filtrate followed by 50cm3 of 0.005M potassium iodate solution 0.5g of potassium iodide.  The liberated iodine was titrated with 0.005M standard sodium thiosulphate solution with constant stirring until the mixture turned yellow. Then 5cm3 of 2.0% of starch solution was added and titration continues until the solution changed from blue to colourless. Volume of the thiosulphate was recorded (Lau and Nina, 2001).   Short Communication Nigerian Journal of Basic and Applied Science (June, 2012), 20(2): 182-184 183 Determination of Loss on Ignition 1g of each sample were taken on weighed crucible and heated in a muffle furnace at 11000C for 30 minutes, cooled in a desiccators and weight difference were recorded (CCNN, 2010).  X-ray Analysis of the Sample 1g of lithium bromide was weighed into three (3) different crucible of the fluxer machine and 1g each of the calcined cement added into the crucible containing the lithium bromide. The mixture were melted and cooled as a glass seats, the glass seats formed were inserted into the X-ray machine to detect the percentage of compound presents in the sample after standard samples were used to calibrate the equipments.   Mineral Content of the Cements The mineral content of the cements were calculated based on Bogue’s formula as outline by Taylor (1990). C3S = 4.07CaO -7.6024SiO2 – 6.7187Al2O3 – 1.4297Fe2O3 C2S = -3.07CaO +8.6024SiO2 + 5.0683Al2O3 + 1.08Fe2O3 C3A = 2.6504Al2O3 – 1.692Fe2O3 C4AF = 3.0432Fe2O3 AAS Analysis Heavy metal analysis was done using atomic absorption spectrophotometer using direct air-acetylene flame at suitable wavelength for each metal (Basset et al., 1997). Standards were prepared form 1000mg/kg stock solution of the metals.  RESULTS AND DISCUSSION The results of the analysis carried out on the samples as shown in Tables 1-3. As shown in Table 1, the percentage compositions of the various major and minor constituents of the cement samples are within the specifications of American Standard for testing materials (ASTM C150). This means that the cement samples were of certain quality.  The SiO2 content for all the samples is in the range of 19.07 – 22.33% with Ashaka recording the highest value i.e. Ashaka > Sokoto > Wapco > Dangote > Burham. SiO2 content is an index for fineness or coerciveness and it determine the grindability of the cement clinker, level of water intake and strength of concrete (Frias and Sanchez, 1995).   Table 1: Percent composition of major constituent of the cement samples by XRF method. Parameter Ashaka Burham Dangote Sokoto Wapco CaO 62.85 ± 0.05 56.17 ± 1.01 64.86 +0.04 64.53 ± 0.02 65.22 ± 0.01 SiO2 22.33 ± 0.02 19.07 ± 0.88 19.96 ± 0.05 20.64 ± 0.14 20.04 ± 0.07 Al2O3 5.87 ± 0.05 5.30 ± 0.45 6.05 ± 0.02  5.40 ± 0.04 5.22 ± 0.05 Fe2O3 3.32 ± 0.01 3.15 ± 0.60 2.99 ± 0.01 3.99 ± 0.01 3.53 ±  0.02 MgO 0.71 ± 0.02 0.74 ± 0.12 1.26 ± 0.01 2.35 ±0.01 3.03 ±0.03 SO3 2.17 ± 0.01 1.14 ± 0.06 1.99 ±0.01 1.77 ±0.04 1.62 ± 0.01 P2O3 0.22 ± 0.01 0.26 ± 0.01 0.24 ±0.02 0.52 ±0.01 0.32 ± 0.01 K2O 1.04 ± 0.02 1.10 ± 0.03 1.09 ± 0.01 0.26 ±0.01 0.26 ± 0.01 Free CaO 1.59 ± 0.05 1.77 ± 0.07 2.15 ± 0.04 2.33 ± 0.04 1.02 ± 0.01 LOI 8.91 3.33 7.48 5.80 4.57  Dangote cement had the highest Al2O3 content which will lead to high content of C3A (Table 2) that contribute to early strength development, while WAPCO cement had the least Al2O3 content. Thus more setting decelerating additives are needed for Dangote in a long period of cementing job. Ashaka shows the highest LOI value which is as a result of carbonation and impurity of free lime and free magnesia due to exposure to atmosphere. Ashaka also had the highest value of SO3 and Burham the least SO3 content which also favours formation of C3S mineral compound which is responsible for initial set and early strength? The lower the SO3 value the better (Taylor, 1990). Sokoto cement shows the highest percentage of Fe2O3 as free CaO. The Fe2O3 is one of the parameters responsible for cement colouration which explain why Sokoto Cement is darker grey than all the cements. High free lime content results in expansion due to formation of Ca(OH)2, Sokoto cement is therefore unsound due to the higher content of free CaO.  In the hydration of the cement powder, it is C3A that causes the sudden hardening of the cement paste. Hence it is usually retarded by addition of gypsum. High amount of C3A is undesirable. The C3S and C2S hydrate to form the calcium silicate hydrate that brings about the adhesive and the cohesive strengths of the cement structure (Ahmed et al., 2009).   Ibrahim et al.: Assessment of Pollution Potentialities of some Portland Cement 184 The calcium aluminoferrite (C4AF) does not have significant role in the hydration of cement. However along with C3A, it serves as a reservoir for the removal of some deleterious ions like Cl- and 2-4SO that cause the rusting of steel reinforced concrete (Taylor, 1990).   The concentration of toxic heavy metals in the cement samples as shown in Table 3, exceeded the maximum allowable concentration limit (Co 0.01, Mn 050, Ni 0.02, Cr 0.05 and Cd 0.003 ppm) stipulated by World Health Organisation (WHO, 1990), and US Environmental Protection Agency (USEPA, 1974).  Table 2: Mineral Composition of Cement Samples (%) Sample  C3S C2S C3A C4AF Sum Ashaka 35.70 37.07 10.00 10.09 93.49 Burham 42.91 29.94 12.51 11.08 96.44 Dangote 56.64 12.98 11.00 9.07 91.69 Sokoto 54.39 18.14 7.57 12.13 92.23 WAPCO 68.12 6.08 7.89 10.72 92.91  Table 3: Heavy metals Content in Cement Samples (ppm)  Samples  Co Mn Ni Cr Cd Ashaka 11.31 12.77 4.22 0.69 2.30 Burham  10.94 8.04 3.65 0.97 2.80 Dangote 11.78 12.32 6.98 1.27 3.05 Sokoto 12.60 6.67 7.93 2.64 2.52 WAPCO 10.76 7.82 4.22 0.55 2.37  CONCLUSION  The result of the analysis indicates that the cement samples under study are generally good for concrete work especially where no other special properties are required. Burham seems to be the best one having the lowest SO3 and free lime content and highest percentage of C3A. More so, the heavy metal content recorded for Burham is also added advantage. Generally, the heavy metal content in all the samples is above the stipulated tolerance.  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Assessment of Pollution Potentialities of some Portland Cement

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Assessment of Pollution Potentialities of some Portland Cement

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