The enhanced adsorption of cadmium on hydrous aluminium(III) hydroxide by ethylenediaminetetraacetate

The effect of co-precipitation on cadmium(ii) adsorption on hydrous aluminium(iii) hydroxide in the presence of a range of chelates

“…In many of the previous studies, especially those involving aluminium, either aged or dried samples or rehydrated aluminium oxide were studied which behave differently from freshly precipitated systems. For example, the adsorption of copper, nickel and cadmium was enhanced by the presence of EDTA at pH 7 10,11 with freshly precipitated aluminium hydroxide but no comparable effect was reported in similar experiments with g-alumina. 12,13 Cadmium in an equimolar mixture with EDTA, moreover, was more strongly adsorbed as the pH 10,11 increased although the trend reported previously for g-alumina was exactly the reverse.…”

“…For example, the adsorption of copper, nickel and cadmium was enhanced by the presence of EDTA at pH 7 10,11 with freshly precipitated aluminium hydroxide but no comparable effect was reported in similar experiments with g-alumina. 12,13 Cadmium in an equimolar mixture with EDTA, moreover, was more strongly adsorbed as the pH 10,11 increased although the trend reported previously for g-alumina was exactly the reverse. 14 In this paper, we show that the changes observed in the presence of EDTA are common to a wide range of EDTA like chelates.…”

“…The computer model used to simulate the adsorption reactions was developed using Microsoft Excel and copies are available from the principal author on request. Details of the calculations and the procedures used have been published previously 11 and are further discussed below.…”

“…Throughout the text, the equilibrium constants for each reaction (x) are denoted by K x . Reaction (8) was not originally included 11 in the equilibrium set because of its supposed trivial contribution to the adsorption equilibrium. Subsequently it was realised that Al(OH)(edta) 2À did have a marked effect on the absolute equilibrium concentrations and consequently on the absolute value of the fitted constants K 3 , K 4 and K 5 .…”

“…14 In this paper, we show that the changes observed in the presence of EDTA are common to a wide range of EDTA like chelates. The model proposed 11 to explain the EDTA adsorption, is shown to be capable of predicting the behaviour of all the systems studied apart from PhDTA. Fig.…”