Two organophosphorus compounds, sodium di-(n-octyl) phosphinate and sodium
di-(n-dodecyl) phosphinate, were synthesized and purified. Lead was precipi
tated from aqueous nitrate and chloride solutions with sodium di-(n-octyl)
phosphinate (NaL) in the form of PbL2(s). The effects of the feed pH. conce
ntration of chloride, concentration of calcium, and of the chain length of
the precipitating agent on the removal of lead were investigated for mole r
atios of NaL to lead between 0.1 and 6.5. Adding acid to the feed solution
reduced the removal of lead as some of the phosphinate precipitated in the
acid form as HL(s). The removal of lead was not affected by the presence of
chloride or calcium in the feed solution, up to mole ratios to lead of 250
and 2.75, respectively. The residual lead in solution was reduced by incre
asing the length of the alkyl group of the phosphinate to dodecyl. Over 99%
of the precipitating agent was recovered by adding NaOH to the precipitate
, and then contacting the solution with diethyl ether to extract the reagen
t. The lead was completely recovered from the PbL2(s). Lead-free precipitat
ing agent, and an aqueous solution of lead at a concentration 100 times its
concentration in the feed, were obtained. Using measured solubility produc
ts of the precipitates and literature values of the stability constants for
the expected reactions, the removal of lead, the loss of precipitating age
nt, and the equilibrium pH were calculated. (C) 2000 Elsevier Science B.V.
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