Effect of total aluminum concentration on the formation and transformation of nanosized Al13 and Al30 in hydrolytic polymeric aluminum aqueous solutions

Influence of total aluminum concentration (CAlT) on the generation and transformation of nanosized Al-13 and Al-30 in hydrolytic polyaluminum aqueous solutions was investigated using high field Al-27 NMR and time-developed Al-Ferron complex colorimetry. When prepared at the optimal basicity (B) of Al-13 generation and 80 degrees C, the Al-13 species in polyaluminum solution tends to further polymerize and convert to Al-30 and higher polymers when CAlT > 0.2 mol(.)L(-1), but Al-13 does not convert to Al-30 quantificationally, as the formation of Al-u from Al-13 and Al-30 is accelerated in the same way. The conversion rate of Al-13 is accelerated by the increase in CAlT. When CAlT > 0.75 mol(.)L(-1), Al-13 content decreases rapidly, and Al-30 content increases continuously and becomes the dominant nanometer polynuclear aluminum species. Al-m is one of prerequisites of Al-13 conversion to Al-30. When CAlT increases and B reduces, the polymerization rate between Al-13 and Al-m increases, and at the same time, the dissociation reaction rate of Al-13 and Al-30 by H+ also increases. The latter becomes the dominant reaction in polyaluminum solution with low B value, so Al-30 decreases with the increasing CAlT. The hydrolytic polyaluminum solution with Al-13 content beyond 80% can only be prepared under the condition of CAlT < 0.5 mol(.)L(-1) and optimal B value.