Comparing water treatment processes lifetime risks using ORE

Comparing water treatment processes lifetime risks using ORE

Comparing water treatment processes lifetime risks using ORE (© Riskope) offers unique advantages to owners, regulators and the public.

As a matter of fact:

• ORE is a convergent quantitative risk assessment methodology. Convergent means that ORE looks simultaneously at all hazard sources. Thus it avoids pitfalls common in “silo-ed” approaches . It also covers a wide spectrum of hard and soft consequences (direct, indirect).
• ORE is scalable, meaning that it can follow a project from pre-feasibility to grave without any loss of information. Meanwhile the hazard and risk register gets more and more detailed as the project evolve.
• ORE hazard and risk register is drillable. That means it allows the creation of specific dashboards. We can custom-tailor them to suit the needs of a project’s stakeholder, on a need to know basis.

At Riskope we have recognized the need to include water treatment in mining systems as witnessed by the more than twenty years old scheme in Fig. 1.

Fig.1 Tailings Management System Generic Layout

Lately BioteQ  asked us to perform a comparative ORE preliminary risk assessment on two water treatment alternatives, namely Lime and ChemSulphide®.

We analyzed three time horizons, i.e. short, medium and long term  for each alternative with “time-invariable” consequences.

We used four Success Criteria Definition for the competing processes, i.e.:

• Meet effluent limits established by regulatory agencies for all anticipated contaminants.
• Not cause acute fish toxicity – even a single rainbow trout kill- during the standard 96 hrs lethal toxicity test.
• Ability to adapt to changes in feed water composition. Anf finally,
• Minimize the generation of waste residues that constitutes potential long term liability.

Finally, we considered the consequences for failing any of the above criteria (i.e. the consequences of failure) identical for the 4 criteria.

Hazard Identification, probabilities and uncertainties

We performed a functional analysis and developed a scheme for both processes using 7 macro elements each as follows:

• Reactor(s)
• Reagent supply & delivery to reactor(s)
• Solid/liquid separation
• Effluent polishing
• Control/monitoring
• Solids handling/disposal and finally
• Solids recycle & conditioning

In total we described 26 hazards, potentially hitting one or more of the system’s macro-elements.

We based probabilities estimates on experience as well as using the ORE transparent process, for the short, medium and long term.

By using ORE (© Riskope) one can introduce uncertainties for existing and new facilities. In the result (Figures 2-5) displayed below we consider an “average” case for the sake of the example.

Results yielded by comparing lifetime risks of water treatment processes using ORE

Fig. 2 Comparing lifetime risks of water treatment processes using ORE (© Riskope) results from a preliminary analysis of Lime vs. ChemSulphide® processes at short, medium and long term. The vertical are represents the total risk. Each column is split in the risks generated within a macro-element.

Figure 2 shows that not only are the risks of the two processes widely different, but their variation with time follows significantly different patters: whereas the ChemSulphide® risks slowly increase with time, those of Lime display a sharp increase, as shown in Figure 3.

Fig. 3. Same results as in Fig. 2 with long term trends displayed as blue arrows.

Due to the drillable nature of ORE hazard and risk register it is possible to understand what causes, for example, the total risk in a given scenario, within a selected macro-element (Fig. 4).

Fig. 4 Here the same results of Fig. 3 are displayed with one addition. For the macro-element control/monitoring of the Lime Short Term scenario the “local hazards” are listed and the related risk components are displayed.

Finally, still to illustrate what the ORE drillable hazard and risk register allows to perform, Fig. 5 shows the relative quantitative total risks for the two alternatives and three terms, after excluding control/monitoring.

Fig. 5 Relative quantitative total risks for the two alternatives and three terms, after excluding control/monitoring.

Conclusions

Comparing lifetime risks of water treatment processes using ORE (© Riskope) offers unique advantages to owners, regulators and the public. In particular, thanks to ORE architecture it is possible to have orderly, rational, unbiased and transparent debates on innovative alternatives. Indeed, uncertainties can be openly discussed and included in the analyses. The scalability of ORE allows to follow any project from cradle to grave, no matter how many decades the service life, closure and post-closure will last.

Tagged with: convergent, lifetime risks, mining systems, quantitative, risk assessment methodology, Success Criteria Definition, water treatment process

Category: Consequences, Mitigations, Optimum Risk Estimates, Probabilities, Risk analysis, Risk management