MATERIALS HANDLING
: “Neither of these applications operated the chosen membranes within the recommended operating windows published by the manufacturers, but both were technically and commercially, very successful and both exceeded the forecast performance used to justify the project capital expenditure… It appears likely that membranes will be applied in a broad range of applications to improve process outcomes.”
the following comments in a paper by Darryl Butcher, director of BDB Process, Australia, regarding two membrane plant projects he had been involved with in Africa[3]
CONTROLLING GYPSUM SCALING IN HIGH AND LOW PH WATERS Unlike other types of scaling, CaSO4
removing it without damaging the membrane is challenging, but not impossible. Tis should be done as promptly as possible to prevent the scale itself causing irreversible damage to the membrane surface. CaSO4
scale initially forms needle-
like particles. It can then go on to form platelets and rosettes, which can damage the membrane surface through abrasion. Tis will ultimately lead to indents
and holes in the surface, affecting the membrane’s salt rejection properties and increasing its flux (allowing more ions to pass though). Te correct pre-treatment and effective use of our specialist antiscalants will drastically reduce scaling. However, if feed conditions are constantly changing or if, at some point, the saturation limit of the antiscalant is exceeded, scale will still form.
is pH
independent. Tat means that the addition of an acid or alkali will have no effect in preventing scale formation. Genesys has developed two new antiscalants – Genmine AS26 and Genmine AS65 –
which are capable of inhibiting CaSO4 at both low and high pH (up to x8-10 saturation levels). Genmine AS26 is particularly resilient to acidic conditions, which is rare for an antiscalant. Formulated and perfected through rigorous testing, it can inhibit CaSO4
of x8-10 (Fig. 2) at neutral and alkaline pH values. Tis is particularly relevant for the alkaline cyanide heap leach processes, where membranes are used to concentrate both pregnant and barren liquors. By providing products specific to both acidic and alkaline minewaters, the company is able to provide the right chemistry for potentially any minewater that is affected by gypsum scale.
REMOVING CALCIUM SULPHATE SCALE If gypsum scale has already built up, perhaps due to using ineffective antiscalants or dosing inappropriately,
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at pH values as low at 1-2 (Fig. 1). Tis means that no costly pre-treatment is needed to neutralise mining effluent for the antiscalant to work. Tat should result in CAPEX and OPEX savings, while making it even more feasible to reclaim both metals and clean water from tailings waste. Of course, not all minewaters are acidic, which is why the firm has also developed Genmine AS65, which is capable of inhibiting CaSO4
scale at saturation levels
Fig. 1. Genmine AS26 vs. traditional phosphonate antiscalants at pH 2 (CaSO4 at x7.8 saturation)
Fig. 2. Genmine AS65 vs. traditional antiscalant at pH 7 (CaSO4
at x7.8 saturation)
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