Three series of small pilot scale tests have been carried out at Honeymoon. A series of push-pull tests were conducted first conducted in 1977, using ammonia bicarbonate solutions based on experience in the USA (Dobrowolski, 1983a). A total of 20,000 litres of leaching solution was injected into the ore zone via a single well, and recovered 24 hours later (Dobrowolski, 1983a). The concentrations of uranium proved too low to be considered economic (Dobrowolski, 1983a).During 1979, a further series of push-pull tests were conducted, intended to give an indication of aquifer permeability and the level of uranium that might be extracted during continuous leaching with a 5-spot pattern using sulphuric acid and some minor alkaline solutions (Dobrowolski, 1983a; Bush, 1998). The success of the sulphuric acid tests led to the commitment by the joint venturers involved, and the Draft and Final EIS’s were subsequently released (MINAD, 1980 & 1981).
A continuous trial of In Situ Leaching was first conducted on a small scale at Honeymoon in 1981, after approvals were granted following the Final EIS (Dobrowolski, 1983a). The trial highlighted the problem of possible gypsum precipitation due to high calcium and sulphate concentrations in the groundwater and calcium bound on the clays (Dobrowolski, 1983a). It was found that the ore zone aquifer needed a “pre-flush” with upper aquifer water low in calcium, and a 5-15% bleed to dilute the ore zone calcium concentration (Dobrowolski, 1983a).
A Field Leach Trial consisting of one 5-spot pattern operating at 1 litre per second (l/s) was undertaken during 1982 (Bush, 1998). Although the main goal of the pilot operation was to achieve effective uranium dissolution without any significant plugging of the ore zone (Bush, 1998), this was not achieved and significant operational and environmental problems were encountered.
The leaching chemistry used was sulphuric acid with ferrous sulphate as the oxidant. Such chemistry, with the high iron and sulphate levels involved, is likely to lead to the precipitation of jarosite, a hydrated ferric sulphate mineral with associated cations of sodium or potassium (eg - formula KFe3(SO4)3.9H2O) (Appelo & Postma, 1994). The formation of jarosite has been noted at uranium mines and tailings dams at Elliot Lake in Ontario, Canada, and was thought to involve the action of bacteria (Ivarson, 1973). Consequently, the field leach trial encountered problems with the precipitation of jarosite and fungal growth (Bush, 1998), leading to aquifer plugging, injectivity loss and minimal control of leach solution movement.
A series of documents were obtained in early 1983 from MINAD by the Campaign Against Nuclear Energy (CANE), and they proved that the 1982 trial was closed due to many significant operational and environmental problems (Wecker, 1983a, 1983b & 1983c; Dobrowolski, 1983b, 1983c & 1983d). The trial on the 5-spot test pattern was stopped due to injectivity losses resulting from decreased aquifer permeability, thought to be due to either mineral precipitation, siltation or bacterial growth (Dobrowolski, 1983c).
A core sample was retrieved in October/November 1982, and sub-sampled for detailed mineralogical and chemical analysis (Dobrowolski, 1983c). The dominant problem was quickly identified by separate laboratories as jarosite formation within the ore zone aquifer sediments from reactions with gangue minerals and chemical precipitation from the leaching solutions (Dobrowolski, 1983b & 1983c). Minor amounts of elemental sulphur and the mineral gypsum (CaSO4) were also found (Dobrowolski, 1983c). The reduction of ore zone permeability began almost immediately upon commencement of the field trial, although problems with the analytical accuracy of the onsite Honeymoon chemical laboratory were also noted (Wecker, 1983b).
The formation of jarosite was seen to occur slowly, but it’s effective reduction of the ore zone permeability was cumulative (Wecker, 1983b). The main concern was that if the problem was not resolved, both the trial and future wellfields could be plugged within only a few months of operation (Wecker, 1983b).
The main chemical parameters that can control the formation of jarosite are pH, redox potential (Eh), and the sulphate and total iron concentrations. Initially, the Honeymoon operators were unable to determine from available technical literature what was likely to influence jarosite formation with their specific leaching chemistry (such as pH, redox or iron levels) (Wecker, 1983b).
Dobrowolski (1983c) suggested that the most significant factor in jarosite precipitation during the trial were temporary excursions in the leaching solution pH which produced seed crystals of jarosite and slow precipitation on ore zone gangue minerals at injection pH values higher than 1.8. It was also presented that jarosite formation could be correlated with pH in trial leach solution samples - where the pH rose above 2.2 jarosite could be seen in the sample bottles (Wecker, 1983a; Dobrowolski, 1983b). The formation of jarosite was exacerbated by various equipment failures that saw the pH during the trial rise above 2.3 on several occasions (Dobrowolski, 1983c).
The exact formation of jarosite was considered to arise from either changes in the pH of the leaching solutions or reactions between gangue minerals leading to jarosite growth on quartz or kaolinite. The first mechanism was considerably rapid, and appeared to be dispersed after the pH was adjusted to a lower value, although it was not realised at the time of the field trial that the fine jarosite created at this stage was plugging the well screens (Dobrowolski, 1983c).
The second mechanism was much slower, and at the temperature and pH conditions in the Honeymoon ore zone aquifer, was likely to occur with the order of weeks (Dobrowolski, 1983c). Although jarosite precipitation was noted in some geochemical environments at a pH of 1.0, it was thought that if the pH was maintained below 1.8, this stage of formation could be prevented or minimised to the point where the growth would occur over months, and therefore not interfere with the short-term operation of a wellfield (Dobrowolski, 1983c). Suggested parameters were thus an approximate pH of 1.7, total iron less than 3,000 mg/l and a redox potential of 500 mV (Dobrowolski, 1983c).
In order to verify the above hypotheses, a series of laboratory experiments were begun by Australian Mineral Development Laboratories (AMDEL) in March 1983 (Wecker, 1983a). Upon authorising the AMDEL studies in mid-March, Wecker (1983b) stated clearly that significant uncertainty still remained about the future of the Honeymoon Project. On March 22, 1983, the SA government announced it’s intention to refuse mineral leases for both Honeymoon and Beverley, effectively stopping the projects (Mudd, 1998d). It is unclear if these studies were subsequently completed.
The use of oxygen was also being investigated at this time as an alternative to ferric sulphate (Wecker, 1983a; Dobrowolski, 1983b & 1983c), although it is unclear what stage this reached. This would avoid altogether the jarosite problem, and had been successfully demonstrated by that stage at the Zamzow ISL project in Texas, USA (Dobrowolski, 1983c). The use of oxygen injection systems is now considered routine in the USA and all current ISL mines use oxygen as their primary oxidant.
There has yet to be any public release of documentation or reports on the various field trials of In Situ Leaching conducted at Honeymoon up to and including 1982.
References :
Based on Section 6.3 of Mudd, 1998.
Page last updated August 1, 1998.
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