On the Bangombé plateau, whenever Comilog extracts manganese, the rock is covered with clay. The ore must then be crushed and ground, but also washed. This is the role of the Moanda concentration plant; built on one end of the plateau, it overlooks the Moulili Valley, a natural waterway 31 kilometers long. Located near the river's source, the concentration plant has been discharging its wastewater into the riverbed for nearly fifty years, and this water contains a significant proportion of manganiferous particles. As a result, the Moulili has gradually become filled with ore fines and sludge. In the so-called upstream portion – i.e. the first 7 kilometers of the river – the deposits, which can reach up to twenty meters in places, have altered the course of the water flow.
The CIM: a plant for the restoration of the upstream section
As the years and decades passed, it became increasingly necessary to put an end to this practice, which began in 1962. But also, to restore the river. So, what was to be done? In the 1990s, Comilog launched a series of studies, which led to the development of a new process for extracting ores. This process allows the manganese fines discharged into the Moulili valley to be sold. In other words, technology has made it possible to repair nature, but also to.... sell the ore collected from the river.
The decision was taken to build an enrichment plant and a pelletizing unit: the Moanda Industrial Complex (CIM) thus began operating in January 2000. Its role: to separate the richest grains from the poorest, and then to enhance their value. "Located on the downstream portion of the Moulili, the CIM is intended to collect, by means of shovels and trucks, the old waste rock from the concentration plant and thereby clean up the river," explains Christian Boupassia, geologist at Comilog, who worked for several years for the complex. A target has been contractually agreed with the Gabonese authorities: the ultimate removal of all sediments from the upstream portion of the Moulili until the original natural clay soil has been restored. With 170 employees currently, the CIM is operating at full capacity. Last year, 1.5 million tonnes of sediment were processed. 500,000 tonnes were sold.
However, at the same time, residues from the concentration plant have continued to be dumped into the Moulili valley, particularly in the upstream portion of the valley. As a result, the riverbed has been gradually buried. To remedy the situation, Comilog decided in 2010 to build an industrial pool on the former mining wastelands of the Bangombé plateau. Discharges from the concentration plant have since then been made into sedimentation tanks that recycle the water from the site. This operation marked the end of the dumping of concentration plant residues into the Moulili.
A swamp excavator for restoring the downstream and upstream stretches of the river
However, the restoration of the river is not yet complete. The time has come to take care of the downstream section. The impetus for this new initiative stems from the holding of a major environmental seminar in Moanda in 2014 by Comilog and the Group's Communications and Sustainable Development Department, which brought together politicians, scientists and NGOs. The event was an opportunity to dispel the misgivings of the local population about Comilog's operations: it was emphasized that manganese is neither soluble in water nor absorbable by living organisms.
In addition, the parties agree together on the method of restoration to be used on the downstream section of the river. A goal was set: to restore the channel of the watercourse, i.e. the flow of the river in its original bed. After research to find the former course of the river, restoration work began in 2018. To carry out this meticulous task, Comilog acquired a swamp excavator at a cost of 800,000 euros. Mounted on floats, the machine is able to remove the sediments that have silted up the river and lower the level of the sludge, allowing the watercourse to return to its original bed. As the restoration of the original channel must be carried out from downstream to upstream, it was decided that the marsh excavator would begin its work on a section located 1.6 kilometers from the beginning of the downstream Moulili.
Christian Boupassia explains: "The bulk of the work has now been done on this portion, and it is now a matter of applying the finishing touches. With the upcoming completion of the restoration of this part of the downstream portion, the teams will be able to tackle the second portion that requires the use of a swamp excavator." The focus is now on restoring the 2.4-kilometre long channel of the final stretch of the Moulili River upstream. This second phase will start as soon as the annual maintenance of the swamp excavator – indispensable after two thousand hours of operation – has been completed. Thereafter, the lengthy job of restoring the Moulili River will thus be able to resume.