The Superintendency of the Environment (SMA) has issued provisional measures against Minera Las Cenizas due to a tailings spill at its plant in Cabildo, Valparaíso Region. The incident, caused by heavy rains on June 13, caused the tailings to exceed the emergency pools and reach the Rincón del Chinchorro stream, also affecting the La Ligua River. This river is crucial for irrigation in an area with water scarcity.
The regional delegate, Sofía González, and the provincial delegate, Luis Soto, confirmed the seriousness of the situation and started meetings with the mining company and the community to take urgent measures. In addition, the Las Cenizas mining company has begun remediation and diagnostic work to determine the causes of the slide in the retaining wall.
Through a public statement, the Las Cenizas Mining Group provided details about what happened, stating that work was done until “technically verifying that the slip on the confinement wall did not affect, in any way, the physical stability of the paste and therefore, the total stability of the deposit.” “The slide on the upper part of the wall that generated water runoff into the containment pools, which were saturated by the flow discharging into the stream, as contemplated in its authorization.”
The SMA requires that the mining company present an action schedule, repair the wall slope in 15 days, clean the tailings from the water courses, and monitor the water quality at specific points. Authorities continue to investigate the incident to prevent future environmental risks.
While this news is ongoing, we, as the PMC Communications team, want to interview our CEO, Luis Bernal, Consultant on thickened tailings and QP in Metallurgy, to obtain a technical look at what happened last June 13 at Cabildo.
- What was your first impression of what happened in the Las Cenizas Tailings Deposit Accident on June 13?
On Friday, June 14th, the last day of the Tailings 2024 Seminar, the news about the Las Cenizas tailings deposit accident was discussed at that conference. The audience expressed concern because this technical event is dedicated to learning about and analyzing the latest developments and best practices for controlling and monitoring conventional, thickened, paste, and filtered tailings to improve the conditions of the mining industry’s tailings in Chile.
- We understand that the tailings deposit at Minera las Cenizas is of the paste tailings type. What do you think about how this system faced this mega rain event?
I would like to emphasize that in response to the first alarming news on Thursday night, the photographs and videos that were published show that thanks to the implementation of an innovative and unique technology for the time (this facility was built more than 15 years ago), the design of the Las Cenizas Paste Tailings withstood this mega rain very well, and much greater damage or consequences to the tailings deposit were avoided.
It is important to highlight the innovative vision of Minera Las Cenizas, a Chilean mining company, ahead of its time, not only with tailings in Pasta in Cabildo but also with thickened tailings and non-desalinated seawater in its operations in Taltal at the Las Luces Plant.
- What do you mean by saying, “Much greater damage or consequences to the tailings deposit were avoided”?
The videos note that the tailings accumulated all these years are completely contained in the bucket and that the overtopping (flow over the wall) is mainly the excess flow of rainwater over the deposit, which may have carried away a portion of fine solids and generated a crack in the wall. However, despite this break in the wall, the entire mass of compacted paste tailings remained inside the tailings deposit.
In another context, if a conventional tailings dam with a sand wall and a large lagoon of slats inside with a low solids content had been installed in that place, the result would have been a catastrophe. For example, the tragedy that occurred in Brazil in 2019 in the state of Minas Gerais due to the rupture of the Vale mining company’s conventional tailings dam precisely with an extreme rain event, which left dozens dead and hundreds missing.
A thickened paste tailing has unique characteristics that make it more sustainable and safer than conventional tailing. The thickened paste tailing has a humidity of around 15% to 18%, which is practically a Non-Saturated tailing; that is, the residual water is distributed over the surface of the tailing particles, and there is no excess free water or pockets of water inside, only the residual humidity. The deposition of tailings in a paste arranged in layers as it loses moisture causes it to densify or compact, reaching a density of 1.7 to 1.8 t/m3; this is a weighty mass that is difficult to move even in an earthquake. Additionally, the ultrafine particles or slats are contained in this compact mass because it is a homogeneous, non-segregated fluid. Characteristics are much superior to conventional tailings, which have low density, are saturated with water, and have fine particles segregated from the rest of the coarse tailings mass, which is a source of particulate matter emission.
- But is the water overflowing the tailings deposit in Las Cenizas just water? According to the news, water analyses will be carried out at specific points, probably around the river channels and in the community.
It is likely that a minimal amount of the solid accumulated in the containment pools has overflowed into the ravine washed away by excess rain. Still, the presence of heavy metals is very unlikely because it requires that the waters contact the tailings for a prolonged period.
- Do you believe that there was an engineering failure in this situation?
As a Consultant on thickened tailings and QP in Metallurgy, I have a lot of confidence in thickened tailings in paste; in fact, I have participated in several projects of this type, for example, in the genesis of the Esperanza project, which was the largest high-density tailings project at the level, worldwide with 95,000 tpd of processing. We understand that this type of accident generates uncertainty in the surrounding communities. Still, we must consider the extreme conditions in which this situation occurred and the fact that there will probably be technical safety solutions to control these mega-events. Predictive models estimate these extreme centennial or millennial rains, which can indicate rains 10 or 100 times larger than a typical rain, for which civil work can carefully put in place diversion channels to divert the rainwater away from the tank or design higher walls to contain rainwater within the same tank.
In summary, the Minera Las Cenizas paste tailings deposit withstood this mega rain event quite well, and thanks to the technology used, a tragedy was avoided.
Chilean engineering, authorities, and technical services such as Sernageomin should draw lessons from this event to promote paste tailings deposits instead of conventional tailings in Chile for their excellent hydraulic stability and additional advantages, such as stability, non-infiltration, lower water consumption, and lower generation of particulate matter.
Disclaimer
This interview represents the opinions of the interviewee. This content should not be taken as regulatory advice, advisory, or a final determination. The content found on this website is for informational purposes only.
