Membrane and Deposit Characterisation

The method was used to measure the size of primar) hematite colloids (see Appendix 3) and the solubility of organics in the presence of calcium. The latter results can be summarised in a number of points. Firstly, no particulates were measured for FA. FA was prepared ar pH 3, pH 6, in the presence of 75 mM NaCl, and in the presence of 25 mM CaClz at pH 8 and 10. A regation or precipitation were not observed under any of these conditions. This indicates that the interaction between FA and calcium is minimal and that FA is vety soluble, even at high salt conditions. 

For HA, at low pH (3.5), particulates were measured in the absence and presence of calcium. Calcium increased the measured particulate size, indicating aggregation of organic colloids. At pH 8 particles formed in the absence of calcium, which shows that there may be some undissolved HA. At pH 10, no particulates were measured and the HA was fully dissolved. Once calcium was added at pH 10, particulates were measured, possibly confirming the co-precipitation of organics with calcite. In the presence of 25 mM calcium, particles are smallest at pH 8 and largest at pH 3.5. Organic concentration did not have a measurable effect on the size of the colloids, and at 25 mM CaCl 2 particles formed at 25, 50, and 75 mgL HA as DOC. 

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