Mining and filtration: a perfect marriage for a cleaner industry

By on July 7, 2017

Nowhere in the world is responsible mining taken so seriously as in the Philippines. Environmental issues are the most critical. Even if it is difficult to think of mining as a “green” industry, it is possible to reduce the impact on the environment, making it more sustainable and therefore providing only benefits to the communities that will rely on it.

When talking about responsible mining, several aspects needs to be analyzed and considered in the management of a beneficiation plant. The most impacting ones are tailings and water handling. Indeed, tailings and process water may contain dissolved chemicals and heavy metals, most commonly associated with acidic water. Therefore, environmental contaminations due to seepage or leakage are a serious problem.

Good water management means reducing, as much as possible, water intake to the plant and discharge to the environment.

The key is maximizing water recycling to minimize the interaction between the mine and the hydrogeological surrounding, especially in catchments and watersheds areas.

The recent disasters at Mount Polley (Canada) or Samarco (Brasil) demonstrate too clearly how dangerous a tailings dam could be and what the associated risks of a failure of such structures can be.

There has been great interest in thickened/paste tailings in recent years, but such tailings management facilities still need to be “contained” because of the residual moisture left inside. However, thickened/filtered tailings can be stacked.

Simply put, this involves a thickener, followed by a filter press and then some form of bulk handling system to move the filter cake to the “stack”. This can be front-end loaders and trucks, stackers, conveyors, or any suitable combination of common bulk handling systems. The deposited material is compacted to form an unsaturated tailings deposit. This form of tailings storage produces a stable deposit usually requiring no retention bunding. It is generally referred to as a “dry stack”.

Filtering the large tailings slurry flowrates of a mine is not easy but the DiemmeÆ Filtration filter presses , a brand of Aqseptence Group, are the prefect answer to this demanding task.

With several hundred GHT filter presses operating in the most demanding applications typically found in the mining and metallurgical industry, we are the leading company in pressure filtration technology.

In particular, the large GHT2500 is now the state-of-the-art for tailings dewatering with more than 50 units in operation and another 30 going to be commissioned soon. The GHT2500 is by far the largest filterpress successfully operating and is the recognized benchmark.

A few numbers about this monster-size filterpress will give an idea of their typical performance: a maximum length of 26 meters; 4.5 metres wide and 5.5 metres high; a GHT2500 can host up to 230 plates for a maximum filtration area of 2000 m2 and 43 m3, meaning a productivity up to 200 tons/hour of high-filtration-rate tailings.

The distinguishing feature of the DiemmeÆ Filtration GHT filter press is the plate pack closing system: the four hydraulic cylinders in a pull-to-close configuration that maximize the sealing of the plate pack and minimize the stress transmitted to the frame and support structure even in the demanding conditions of the mining industry.

The plates and the moving head are hung on one or two overhead beams sliding along it for opening/closing. Depending on the type of material (high or low filtration rate) a plate-by-plate or an accordion opening system can be used to bring the highest benefit to the process.

Several devices smooth the filtration process making the GHT a totally automatic system. The cake shaking mechanism for perfect release of the filtered cake and two different washing system (low pressure and high pressure) keep the cloths clean from the superficial dust and from the fines that would tear and blind the filtration media, extending the lifetime and reducing the consumables and the downtime of the equipment for maintenance.

In particular, maintenance needs are taken very seriously at Aqseptence Group. Indeed our unique system enables rapid cloth changing (less than a minute per cloth) that will reduce the downtime for maintenance of the equipment. Moreover, the DiemmeÆ Filtration GHT filter press could be provided with a lateral platform for easy access to the filter and easier maintenance.

The filters are totally controlled by PLC with a user-friendly HMI for simplified monitoring and controlling.

The distinguishing features of this filter are not limited to the structure, but also the plates are very special: our plates have a unique double-feeding system and a special draining systems that permits a very uniform and smooth filling of the chambers with improved fluid dynamics.

This helps to lower the moisture level and to save energy when very low levels of moisture are needed.

This is a typical case in the dewatering of mining tailings as unsaturated cakes are crucial for a stable stack where we can easily achieve low moisture such as 14-15% for copper/gold tailings or 30% for aluminum or nickel ones.

This is also the standard in the filtration of mining concentrate where a very narrow window of moisture presence is required for avoiding liquefaction and dust formation during shipping: in this case it is possible to reduce the cake moisture to as low as 5-8% w/w (depending on the type of concentrate) while controlling it precisely with the aid of load cells underneath the filterpress.

Last October, we hosted an Open House event at our Italian headquarters with customers from every part of the world (US, Australia, Philippines, Russia, Indonesia, India and many more – in fact, more than 38 different nationalities) presenting our huge GHT2500F to be used in the filtration of leached bauxite tailings (red mud – a tricky filtration that deals with hot, extremely caustic and sticky slurry).

CEO Rosario Tagliavini said: “If you ask me what we do best, it is custom-made large and heavy-duty equipment for the mining and process industry. Filtration is a complicated matter with many variables, so you need to have expertise, knowhow and analytical abilities.” PRJ

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