memo To:
Simon Drummond (Hydrobiology)
From:
Peter Papa
CC:
Peter Mellor, Malcolm Paterson, Putri Leony
Date:
21/12/2022
Re:
Mt Morgan Hydrobiology – Water quality results when adding final tailings to OCP water (HYD-01)
This technical memo presents the results of the laboratory water quality test after contacting final ReCYN tailings with OCP water .
1) Aim The aim of this test was to determine any changes to the OCP water quality after adding final ReCYN tailings to the OCP. This was determined by conducting a laboratory bench-scale test, where OCP water was contacted with the final ReCYN tailings residue to determine any changes in water quality (ie; properties, anions and dissolved cations). 2) Method A 1kg sample of the No.2 Mill final ReCYN tailings residue from previous laboratory ReCYN leach and adsorption tests (ie; Cycle Test #3) was first slurried in water from the OCP (32% w/w solids). The slurry was agitated overnight in a baffled vessel using an overhead stirrer (ie; 15 hours agitation time). A full water analysis was then conducted on two OCP water samples (ie; one sample of the original OCP water used and one sample of the final water after contact with ReCYN tailings). These analyses were then compared to determine the change in water quality (ie; changes to the water properties, anions and dissolved cations). 3) Results The following table summarises the main OCP water analysis results, before and after being contacted with the final ReCYN tailings (full laboratory assay report attached at the end of this Memo). The results indicated a minor increase in pH and water hardness, possibly due to some lime still being present in the residue from the original cyanide leach process. This could have also caused the reduction in sulphates, via the formation of gypsum (CaSO 4 .2H 2 O) which would have subsequently been filtered out. The main dissolved cation to increase was iron, possibly due to insoluble iron species in the original cyanide leach process (ie; operating at a high pH of 10), which then re-dissolved when contacted with the acidic OCP water. There were also significant reductions in the aluminium, copper and lead solution concentrations, possibly due to these being adsorbed by the final tailings solids (ie; equilibrium effect due to reduced concentrations on the original leached tailing solids). There were negligible differences for the remaining anions and dissolved cations.
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