Transfer of Some Major and Trace Elements From Phosphate Rock to Super-Phosphate Fertilizers

Transcription

1 Transfer of Some Major and Trace Elements From Phosphate Rock to Super-Phosphate Fertilizers H.I. El-reefy a, A.A. Bin-Jaza b, M.E.Zaied c, and H.M. Badran c,d,* a Hot Laboratories Center, Atomic Energy Authority, Cairo, Egypt b Physics Department, Faculty of Science, University of Hadhrmout for Science and Technolgy, Al- Mukalla, Yemen c Physics Department, Faculty of Science, Tanta University, Tanta 31527, Egypt d Physics Department, Faculty of Science, Taif University, Al-Haweiah 21974, Taif, Saudi Arabia Received: 19/11/2013 Accepted: 20/12/2013 ABSTRACT This study assesses the transfer of some major and trace elements from phosphate rock (PR) to single (SSP) and triple (TSP) superphosphate fertilizers. Samples from a fertilizer plant and local market were collected and analyzed using inductively coupled plasma spectrometer. Cluster analysis indicated that the innerrelationship among the concentration of the elements in PR, SSP, and TSP are different. Only one element (Mo) has concentration in SSP higher than phosphate rock. The production process of these two types of superphosphate leads to transfer higher portion of Mn, B, Cu, Mo, Sr, and V present in the phosphate rock to SSP than TSP. The potentially hazardous element Cd is also transmitted more to SSP than TSP, and Cr is equally transferred to both types. The mean elemental concentrations normalized to the percentage of P 2O 5 demonstrate that for most elements they are the higher concentrations in SSP are linked to the phosphate contents. Keywords: Phosphate rock; Phosphate fertilizers; major and trace elements INTRODUCTION Phosphate rock is a sedimentary rock containing naturally occurring form of phosphate minerals, usually apatite, which can be commercially exploited, either directly or after processing, for commercial applications. Sedimentary phosphate deposits in Egypt belong to the Cretaceous age (1). Composition of phosphate rock largely depends on its type and origin. Phosphate rock is mainly used for the manufacturing of phosphate fertilizer. Phosphate rock is insoluble in soils and releases phosphorus very slow. Most of world phosphate rock (PR) output has been delivered to the world fertilizer industry. The remaining production is mainly directed to the animal feed and chemical industries. Fertilizers enhance the natural fertility of the soil or replace the chemical elements taken from the soil by harvesting, grazing, leaching or erosion. Fertilizers containing phosphate have become essential to agriculture. They are used to replenish natural nutrients removed from the soil because of farming and erosion. The concern of increasing consumption of fertilizers in Egypt is because of the environmental problems related to fertilizers, as they can be a major source of non-point source pollution in groundwater, and the accumulation of heavy metals in soil and their release to waters, together with their potential bioaccumulation in the food chain, are among the main problems. * Corresponding author. Tel.: address: hussein_badran@hotmail.com 32

2 Single superphosphate (SSP) is the simplest and oldest of manufactured phosphate fertilizers. Ground phosphate rock is treated with sulfuric acid to produce a product usually containing about 18% P 2O 5. Triple superphosphate (46% P 2O 5) is made by acidulation of phosphate rock with phosphoric acid. Like SSP, TSP is a straight product of the reaction between acid and the rock where no by products are removed from the process (with the exception of fluorine). All potentially hazardous elements contained in the rock and in the acid will be present in the final product. The major raw materials required for manufacturing of SSP and TSP are rock phosphate and sulphuric or phosphoric acid. The phosphate rock is crushed, ground, and treated with sulfuric acid to produce SSP. For making TSP the rock is neutralized with phosphoric acid instead of sulfuric acid. Most of the reactions occur quickly, but they continue slowly over few days. A partially matured superphosphate is formed from the sloppy mix. The solid material is then converted to powder. The reacted mixture can also be granulated (turned into small pellets). The product contains mono calcium phosphate which is soluble in water. The higher solubility of fertilizers in relation to insoluble phosphate rock, allows increasing the benefits of phosphate application. It is identical in both SSP and TSP. Calcium sulfate is present only in SSP because it is formed when sulfuric acid is used. Main difference between triple and single superphosphate is phosphorus compounds content expressed as a P 2O 5. In triple superphosphate it is about three times higher than in the single superphosphate. Reason for this is that phosphoric acid constitutes for additional phosphorus source in fertilizer. The present study gives a detailed chemical analysis of phosphate rock sand commercial superphosphate fertilizers, including major elements and trace elements in order to assess the entire potential contamination of fertilizers. This study was conducted to examine the transfer of these elements from phosphate rock to the manufactured TSP and SSP and change of the inner-relationship of the measured elements because of the two production processes. MATERIALS AND METHODS Evaluate the radioactivity concentrations in soil, sediment, water, and plants were conducted to study the impact of a phosphate fertilizer plant (EFIC company)in Kafr El-Zayat situated on Rosetta branch of the Nile River surrounded by agricultural and urban areas (2). This study also included samples of phosphate rock and fertilizer from the plant. In the present work 8 samples of PR (PR1 PR8) from the same plant and 4 samples (F1 F4) of TSP and 10 samples (F5 F14) of SSP are collected from the storage area before packing inside the plant. In addition, 4 samples (F15 F18) of TSP and 4 samples (F19 F22) of SSP produced by the same company were obtained from the local market. These samples are meant to evaluate the effect of the production processes of SSP and TSP on the transfer of major and trace elements from PR. For the purpose of comparison, samples from a second Egyptian company (Abou Zaabal Fertilizer Company; 11.5% P 2O 5 modified mono phosphate) and phosphate fertilizer produced in India and packed in United Arab Emirates (Triple Super Phosphate 46% P 2O 5), were also investigated. Sample preparation was performed under controlled conditions and a special care was taken to keep the samples and the work place free from dust. Samples were homogenized and powdered. Inductively Coupled Argon Plasma (ICAP 6500, thermo scientific, UK) was used to determine the concentrations of major and trace elements. Major elements included in the present investigation are Al, Fe, and Mn. Oxides of iron, manganese, aluminum and silicon are of great importance in exploration geochemistry due to their ubiquitous occurrence and strong scavenging of metal ions (3,4). Trace elements considered in this work are B, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sr, V, and Zn. The digestion procedure of the samples was performed using a microwave oven. 33

3 RESULTS AND DISCUSSIONS The concentrations of major and trace elements in PR, SSP and TSP are presented in Tables1, 2, and 3. The mean concentrations of 14 elements are also given in each case. The concentrations of all measured elements in phosphate core are considerably homogenous. The calculated Z-scores are within 2.0 in all cases except only two cases; the concentrations of Cd in PR4 (2.07 ) and Pb in PR8 (2.02 ). On the other hand, the elemental concentrations in SSP show more cases that exceeds 2.0. Those cases are; the concentrations of Fe ( 2.32 ), Cr ( 2.37 ), Ni ( 2.29 ), V ( 2.87 ), and Zn ( 2.34 ) in F12, the concentrations of B (2.23 ) in F5, and the concentrations of Co (2.31 ) in F19. Three cases were also found for TSP; the concentrations of Sr in F15 (2.19 ), the concentrations of B in F16 (2.03 ), and the concentrations of Mo in F17 ( 2.07 ). Pb is not included in the above discussion since it was detected in only few samples in each case. The Indian fertilizer has the highest concentrations of Al, V, and Zn and the lowest concentrations of Cd, Cr, and Sr. Abou Zaabal fertilizer has relatively lower concentrations in particularly for Mn and B. The only exception is the concentration of Pb which is the highest among the three companies. On the other hand, SSP from EFIC has the highest concentrations of Cd, Cr, M, and Sr. Many applications require projection of multidimensional data onto some lower-dimensional space. Dimension reduction aims to identify the features in a multidimensional space that contribute to the classification of interest significantly and to retain most of the information of the original data. Cluster analysis represents a wide range of techniques used for combining cases into groups or clusters with similar characteristics, and to better visualize classification in the data (5). Cluster analysis was used to identify the interrelationship among the measured elemental concentrations. The similarity matrix based on relative species abundance for each sample is obtained with a Pearson correlation coefficient as the measure of similarity. The statistical analysis has been performed by means of StatistiXL (6). Throughout this work the correlations will be described as strong (r 0.95), moderate (0.85 r< 0.95) or week (0.75 r< 0.85). Figure 1 shows the hierarchical dendrogram for PR that illustrates the similarity between the chemical parameters. One cluster of elements includes V, Cr, Zn, Fe, Mo, Sr, and Cu. Moderate correlations exist between V, Cr and Zn (Pearson correlation coefficient; r = ). These three elements seem to co-vary with Fe, Mo, Sr, and Cu with decreasing significance. Week correlation exists between Co and Mn (r = 0.82). Ni and Al are weekly correlated (r = 0.76) and have obviously no correlation with the rest of the measured elements. Of the more common potentially hazardous elements associated with phosphate rock and fertilizers is cadmium. It is important to note that the concentrations of Cd in phosphate rock have no clear relation with the concentration of any other element. Figures 2 and 3 show the dendrograms for SSP and TSP, respectively. The general classification structures of PR, SSP and TSP are not in agreement. This is a clear indication that the two chemical processes change the chemical inner-relationship of PR. In the case of SSP, the only cluster of elements with significant correlations is the one that contains V, Fe, and Mn (r = ). On the other hand, week correlations exist among Zn, Ni, Cr, and Co. This cluster of elements may have a correlation with the V, Fe, and Mn cluster. For TSP, the association between Cd, Mn, Fe, and Al is most significant, with bonds to Co and to a lesser degree to Ni, Zn, Cr, and V. The second cluster of association at a lower level of significance was found between Sr and Pb and between Cu and B. 34

4 Table (1): The concentration of major and trace elements in phosphate rock (μg g 1 ). Al Fe Mn B Cd Co Cr Cu Mo Ni Pb Sr V Zn PR PR PR PR PR PR PR PR mean SD SE median SD standard deviation; SE standard error Table (2): The concentration of major and trace elements in SSP (μg g 1 ) Al Fe Mn B Cd Co Cr Cu Mo Ni Pb Sr V Zn F F F F F F F F F F F F F F mean SD SE median India AbouZa abal SD standard deviation; SE standard error 35

5 Table (3): The concentration of major and trace elements in TSP (μg g 1 ). Al Fe Mn B Cd Co Cr Cu Mo Ni Pb Sr V Zn F F F F F F F F Mean SD SE Median SD standard deviation; SE standard error 36

6 V Cr Zn Fe Mo Sr Cu Co Mn Cd B Pb Ni Al Fig. (1): Dendrogram for phosphate rock clustering of major and trace elements based on the Person correlation coefficient. 0.5 Pearson Correlation Coefficient 0.3 Sr Pb Zn Ni Cr Co V Fe Mn B Cu Cd Al Mo Fig. (2): Dendrogram for SSP clustering of major and trace elements based on the Person correlation coefficient. 0.5 Pearson Correlation Coefficient

7 Cd Mn Fe Al Co Ni Zn Cr V Sr Pb Cu B Mo Fig. (3) Dendrogram for TSP clustering of major and trace elements based on the Person correlation coefficient. 0.6 Pearson Correlation Coefficient 0.4 Concentrations ( g g -1 /%P 2 O 5 ) SSP TSP Phosphate core 10-2 Al Fe Mn B Cd Co Cr Cu Mo Ni Pb Sr V Zn Fig. (4): The mean elemental concentrations normalized to the 1% P 2O 5 in phosphate core, SSP, and TSP. 38

8 To evaluate the transfer of different elements from phosphate rock to any of the two types of fertilizers, the ratio of the concentration of an element (C F,e ) in the fertilizer to the mean concentration of the same element in phosphate rock (C PR,e) was calculated as C R C For most elements, the ratios are less than or close to unity. Only the concentrations of Mo are higher in fertilizer than PR especially in SSP for which the ratio is 2.2. The concentration of Cu in SSP is higher by 6% than that PR. The least elements transferred from PR to the fertilizer are Mn and B. For the rest of the elements, the ratios are between 0.5 and unity. In an attempt to link the concentrations of the measured elements to the phosphate contents in fertilizer, the mean elemental concentrations normalized to the percentage of P 2O 5 in SSP and TSP were calculated (see Fig. 4). The mean elemental concentrations per 1% P 2O 5 for phosphate core are also shown for comparison assuming a 30% concentration of P 2O 5. For all elements, SSP has higher mean P 2O 5-normalized concentrations than TSP and PR. In some cases the differences are not significant such as B and Pb. F, e PR, e CONCLUSION The variation of the concentrations of major and trace elements in PR are confined while the concentrations of some elements have relatively large variation from the mean values for SSP and TSP. Cluster analysis demonstrate that the production processes of SSP and TSP produce different innerrelationships among the measured elements which are also different than that found for PR. The results demonstrate the production lead to build up all elements in SSP more than TSP. REFERENCES (1) A.J.G. Notholt, African phosphate geology and resources:a bibliography, ; Journal of African Earth Sciences: (1991) (2) M.E. Zayid, Study and evaluation of the natural and artificial radioactivity levels in Kafr El-Zaiyat, Ghrbeiya. Faculty of Science, Tanta University. (2012) (3) Chao, T.T. and P.K.Jr. Theobald, The Significance of Secondary Iron and Manganese Oxides in Geochemical Exploration; Economic Geology: (1976) (4) Singh, S.K. and V. Subramanian Hydrous Fe and Mn oxides Scavengers of heavy metals in the aquatic environment; CRC Critical Reviews Environ. Control.: (1984) (5) M.S. Aldenderfer and R.K. Blashfield, Cluster Analysis. Sage Publications, Inc., Newbury Park, CA. (1984) (6) Last time checked Jul. 10,