Phosphorus fertilizers from less pure
sedimentary sources become increasingly important, due to depletion of
phosphorus from igneous rock of high quality. Consequently, robust methods with
potential to remove various types of hazardous elements are required. Among
such impurities, hexavalent chromium (Cr(VI)) is very likely to become a future
challenge. Different industrial ways to treat phosphate rock are currently
being practised, and we have here studied how chromium behaves when using the
nitro-phosphate process.The
reduction mechanism of Cr(VI) in
nitric acid and phosphoric acid solutions was investigated by measuring redox
potential and UV-VIS spectra. The results show that Cr(VI) is not stable in strong
nitric acid solutions.
Reduction of Cr(VI)
species decreased with decreasing temperature, NO2 concentration,
ionic strength and absence of light.These findings support the proposed
reduction reaction:The reduction rate was observedproportional to the nitric acid decomposition: .
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