Effects of Cold Temperature on the Stability of Arsenic Trioxide Roaster Waste Dust in Cemented Paste Backfill
Bibliographic record
Abstract
Giant Mine is a retired gold mine located 5 kilometers north of Yellowknife, Northwest Territories, Canada which operated from 1948 to 2004. Gold ore in this region is hosted in arsenian pyrite and arsenopyrite. Being refractory, arsenopyrite is resistant to cyanidation, thus had to be roasted at high temperatures first. During the roasting process, arsenic-rich vapours were produced that precipitated as arsenic trioxide dust. An estimated 237,000 tonnes of arsenic trioxide roaster waste (ATRW) dust was produced, captured, and stored in underground chambers and mined out stopes. Arsenic trioxide is a highly toxic, bioaccessible, and soluble form of arsenic, therefore it poses high risks to the environment and human health. Due to the quantity of dust, dust-like characteristics, and current storage in subsurface stopes and chambers, the long-term management of the dust is complex. Many methods to stabilize, manage, change, or control the dust have been studied, and the “Frozen Block Method” method was chosen to move forward with. The goal is to freeze the dust and surrounding rock to isolate arsenic and reduce the risk of arsenic release to the environment by water transport. Although this method is promising, it requires ongoing maintenance, and therefore it is suspected to last a maximum of 100 years. Other methods of dust management include in-situ or ex-situ management including pump and treat, bitumen encapsulation, cement encapsulation, vitrification, or chemical stabilization. Solidification and stabilization are used commonly in mine settings and for hazardous waste to encapsulate the materials and reduce the mobility of hazardous compounds. Cemented Paste Backfill (CPB), a mixture of tailings, cement binder, and water, can be used to stabilize arsenic and other heavy metals by physically encapsulating and chemically stabilizing the arsenic through the formation of cement hydration products. CPB has been used in many settings, including northern regions, but it has not regularly been used in cold environments to stabilize mine waste. Due to the ground freezing from the Frozen Block Method, along with discontinuous permafrost around the mine site, and seasonal temperature variations, the CPB may be exposed to freeze-thaw (F/T) cycles, or long-term frozen periods. The purpose of this study is to determine how the exposure to freeze-thaw cycles or cold temperature will affect the stability of arsenic in CPB. Unconfined Compressive Strength (UCS) tests, hydraulic conductivity tests, and micro-CT scanning were used to assess how CPB cylinders with ATRW dust react to F/T cycles and cold temperature curing. Samples were cured at 20°C, 5°C, -5°C and -10°C for 7, 14, 28, 90, and +200 days to assess the impacts of curing time and curing temperature on ATRW-containing CPB samples. Additional samples were cured at 20°C for up to 42 days and then exposed to 0, 1, 5, or 10 F/T cycles. Each cycle consisted of 24 hours at -5°C followed by 24 hours at 20°C. It was determined that after repeated F/T cycles, samples of CPB with ATRW deteriorate and fractures appear in the samples. Samples exposed to 1 and 5 cycles experienced a decrease in UCS in 26% compared to the control group, whereas samples exposed to 10 cycles experienced a decrease in UCS of 49% compared to the control group. Additionally, 10 cycles resulted in an increase in hydraulic conductivity of up to two orders of magnitude. Curing duration and temperature also affect the samples, but less so than the freezing and thawing, and the effects depend on the coupled effect of curing temperature and time. Frozen cured samples resulted in a decrease in strength compared to 20°C, regardless of curing time. CT scanning results indicated that no fractures were formed in frozen cured samples or after 1 F/T cycle, however, after 5 and 10 cycles, microfractures appeared in some areas of the samples. The results of this study conclude that F/T cycles and cold temperature pose concerns to the stability of arsenic in CPB. Using this method in a northern climate may require modifications to the CPB in order to reduce fractures formed and create a more stable paste.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".