Surface force arising from adsorbed diethylenetriaminepentacetic acid (DTPA) and related compounds and their metal ions complexes in alumina suspensions

The zeta potential- and yield stress-pH behaviours of α-Al2O3 suspensions in the presence of diethylenetriaminepentacetic acid (DTPA) were evaluated. DTPA was found to act as an effective steric agent at concentration as low as 0.05 dwb% up to as high as 0.8 dwb%. The maximum yield stress of the suspension was reduced up to 76%. When compared to its lower molecular weight (Mw) counterparts; ethylenediaminetetracetic acid (EDTA) and nitrilotriacetic acid (NTA), this study revealed that DTPA had negligible bridging capability despite having a higher Mw and degree of branching. DTPA, EDTA and NTA were deduced to adsorb lying flat on the particle surface. Chelating EDTA and DTPA to metal ions increased the rigidity of its structures. The [ZnDTPA]3− and [CuDTPA]3− complexes imparted certain degree of bridging between particles. This bridging interaction is quite weak. The chelate structure showed the possibility of particle bridging occurring. However [ZnEDTA]2−, [CuEDTA]2− and [FeEDTA]− do not possessed a structure for particle bridging to occur and as a result they acts as an effective steric agents. The DTPA complex ions have one or two free carboxylate groups to participate in bridging while that of EDTA has none.