Belay Zeleke Dilnesa - Eawag-Empa Library

CHAPTER 3 SYNTHETIC FE-CONTAINING HYDRATES
concentrations from 2 to 1 mmol/l. For the Fe-free Al-monosulfate, a lower calcium
concentration, sulfate and aluminum concentrations were measured. Generally the
aluminum concentrations were 100 to 1’000 times larger than the iron concentrations
which were limited by the precipitation of Fe(OH)3. In the aluminum free sample
(XAl/(Al+Fe) = 0.0), 0.63mmol/l of Al was detected. This indicates that the samples were
contaminated by Al. Additional investigations indicated that aluminum contamination
had occurred during dilution of the samples with HNO3; thus all measurements were
corrected by 0.63 mmol/l Al “blank” value (see Table 19). However, even after this
correction the calculated solubility products of Al-monosulfate and Al-ettringite were
approximately 1 log unit higher than expected (see Table 20).
Table 19 Compositions of Al/Fe-monosulfate after synthesis at 20°C equilibrated for 680 days in
supersaturated condition.
Al/Fe+Al Al Al* Ca Fe K S OH +pH Solid phases
Ratio [mmol/l] [mmol/l] [mmol/l] [mmol/l] [mmol/l] [mmol/l] [mmol/l] present
0 0.63