Ac. Braithwaite et al., AN INVESTIGATION OF EXTRACTION PROCEDURES FOR ASSESSING THE PHOSPHATEROCK RESIDUE IN MULTICOMPONENT FERTILIZERS, Fertilizer research, 34(3), 1993, pp. 223-231
Five chemical extractants-water, neutral ammonium acetate, neutral amm
onium citrate (hot and cold) and alkaline ammonium citrate-have been a
ssessed on their ability to efficiently isolate the residual phosphate
rock present in multicomponent fertilisers without affecting the phos
phate rock. Phosphoric acid-based partially acidulated phosphate rocks
(PAPRs) were manufactured along with several LONGLIFE (LL, single sup
erphosphate to which ''reactive'' phosphate rock is added ex-den) mate
rials for the assessment of these extractants. Each extractant was ass
essed by analysing the resultant residual phosphate rock isolated from
each multicomponent fertiliser and comparing its chemical properties
with the original phosphate rock used to manufacture the products. An
analysis of ''extractable phosphorus'' was also undertaken. X-ray diff
raction analysis was performed on selected phosphate rock residues as
an independent method of examining the extraction techniques. Water an
d neutral ammonium acetate were found to be unsatisfactory for use as
extractants, neither removed calcium sulphate when present, while the
latter also did not appear to extract all the monocalcium phosphate co
mponent. The remaining three extractants all removed soluble phosphoru
s components and ''impurity species'' from the fertiliser products, le
aving the residual phosphate rock relatively unaffected. Residue analy
ses were only slightly modified to those of the original rocks, althou
gh there were some inconsistencies in results obtained using hot neutr
al ammonium citrate. X-ray diffraction analysis showed no significant
differences between residues produced from neutral ammonium citrate or
alkaline ammonium citrate extractions, but water and neutral ammonium
acetate residues confirmed the presence of calcium sulphate in LL and
the presence of monocalcium phosphate in a neutral ammonium acetate e
xtracted PAPR. From this study, cold neutral ammonium citrate and alka
line ammonium citrate appear to be equally suitable for isolating the
phosphate rock from a multicomponent fertiliser, leaving the residual
rock substantially unmodified from the original phosphate rock. Howeve
r, there was a slight preference for cold neutral ammonium citrate due
to its ease of preparation and use.