TITLE:
Analysis of Iron, Scandium, Samarium, and Zinc in Commercial Fertilizers and the Chemistry behind the Stability of These Metals in the Fertilizers
AUTHORS:
Md Sajjadur Rahman, Syed Mohammod Hossain, Mir Tamzid Rahman, Mahbub Kabir
KEYWORDS:
Phosphate Fertilizer, NAA, γ-Ray Spectrometry, Metal-Phosphate Interaction, DFT
JOURNAL NAME:
Journal of Agricultural Chemistry and Environment,
Vol.8 No.3,
August
16,
2019
ABSTRACT: Fertilizers are the indispensable materials for farming and one of the
major components of the current world economy. It is essential to understand
the chemical structures of fertilizers to provide best quality products to the
consumers. In this study, chemical structures of some frequently used
commercial fertilizers (compost, DAP, and TSP) and their phosphate-metal
interaction chemistry were studied employing both analytical and theoretical
methods. Three types of fertilizer samples from the mid-southern part of
Bangladesh were collected to quantify the content of two micronutrient metals
(iron and zinc) and two non-essential metals (scandium and samarium). Neutron
activation analysis (NAA) coupled with γ-ray
spectrometry was employed to analyze the content of the metals where three
standard reference materials, namely IAEA-SL-1 (Lake Sediment), IAEA-Soil-7,
and NIST Coal Fly Ash 1633b, were used. Concentration of Fe (2964 - 24,485)
mg/kg, Sc (3.50 - 11.80) mg/kg, Sm (2.19 - 26.69) mg/kg, and Zn (243 - 4426)
mg/kg were determined in the fertilizer samples. Extremely high concentrations
of Fe and Zn were quantified in some of the compost and phosphate fertilizers
in comparison with other studies of different countries. Quantum mechanical
calculations were performed to understand the molecular level interactions of
Fe and Zn with triple super phosphate (TSP) and diammonium phosphate (DAP) fertilizers
by employing DFT-B3LYP/SDD level theory. Results showed that both Fe and Zn
have high affinity with the phosphate fertilizers, but Fe compound showed
stronger binding affinity than the Zn compounds, which supported the
experimental results. Another interesting finding was that the compounds of Fe
and Zn attached to the oxygen of the phosphate group of the fertilizers by
covalent-like bonding. HOMO-LUMO gaps of the Fe-DAP/TSP complexes were observed
significantly lower than the Zn-DAP/TSP, which also demonstrated that Fe
compound could have higher affinity to attach with the phosphate group of DAP
and TSP fertilizers.