Output SEAP December 2012 / 7

Assarel-Medet JSC Mining and Processing Complex is the first, largest and leading Bulgarian company for open pit mining and the processing of copper ores, providing around 50% of the national production of copper. Assarel-Medet JSC processes approximately 13 million tonnes of ore per year.

PROJECT OVERVIEW

Assarel-Medet JSC owns and operates a copper mine and concentrator in Panagyurishte, Bulgaria. The rural facility occupies a 20 hectare site, 90km south-east of Bulgaria’s capital city Sofia. Concentrator production was approximately 50,000tpa copper in concentrate, with the waste and side rock processed via dump leaching and cementation. At capacity, the old process was producing low commodity, cemented copper containing 60-80% Cu.

Cu SX-TF-EW 3D layout

In 2007, Assarel sought to improve copper production and quality by modernizing the leaching and cementation process. The target was to increase profitability by producing copper cathodes, free of impurities. Another key objective was improving operator safety and working conditions due to the harsh climate and processing involved. The new copper plant design proposed by Outotec consisted of three main process areas - Solvent Extraction, a Tank Farm and Electrowinning (Cu SX-TF-EW).

Assarel proceeded with the new plant, selecting Outotec as the technology supplier and project advisor.

SCOPE

Outotec was engaged to provide an extended technology and supervision service package for this project. The scope comprising of a basic engineering and equipment package

CASE STUDY: ASSAREL MEDET

OrganisationAssarel Medet JSC

SitePanagyurishte, Pazardzhik, Bulgaria

Year2007-2010

ApplicationCopper cathode production facility

Challenge � Compact, housed footprint

� Project schedule delayed by a year due to GFC

� Harsh weather conditions affecting solids concentration and diluting the copper feed concentration

Solution � Extended technology and supervision service package, basic engineering and equipment package, proprietary and key equipment supply, commissioning and start-up services for new Cu SX-TF-EW plant.

Result � Delivery and commissioning within deadline

� Improved working conditions and operator safety

� Production capacity 2,000 tpa LME grade A copper cathode

� Innovative SX mixer-settler designs

� Highly efficient settling rates reducing equipment size by 40% and organic inventory by 30%

Output SEAP December 2012 / 8

for the new copper plant, plus detail design of the Outotec proprietary equipment and delivery of all process equipment. Additionally, the scope extended to include the plant automation system and auxiliaries, such as a pressure air compressor, safety showers and storage tanks.

Within the scope of the extended package, Outotec oversaw and reviewed the detail engineering and construction carried out by the client’s own contractors. The Outotec team also assisted Assarel to specify the demi-water process and the Pregnant Leaching Solution (PLS), purification, heating and fire protection system. To ensure a seamless operation, the client opted for a full training service package, commissioning and start-up services, with post-commissioning support via remote connection between Outotec and the Assarel Cu plant automation system.

The majority of Outotec’s equipment, including process tanks and settler parts, were shipped to Bulgaria as prefabricated modules, greatly reducing construction on site, so negating potential issues with weather and space restrictions. Transformer-rectifiers, electrolyte filters, mixer-settler separation fences and electrowinning cells were also shipped from overseas.

CHALLENGES

The most notable difficulties encountered at Assarel were the harsh weather conditions and mountainous site location. The facility sits adjacent to the open copper mine pit and at 1,000m above sea-level, the exposed site is subject to wind speeds in excess of 25m/s and temperatures below -20�C. To protect the operators and equipment, the new Cu SX-TF-EW plant was totally enclosed. The SX plant footprint is very compact,

with a total floor area of 2,100m2 and the three main process areas, i.e. solvent extraction, tankfarm and electrowinning, needed to be separated by a fire wall.

PARTNERSHIP APPROACH

Assarel provided all pipelines, instruments and valves with the remainder of the detail engineering and construction carried out by Bulgarian companies. With numerous contractors and equipment suppliers, project management can quickly become difficult, particularly where technical issues get lost in translation Outotec, however was focused on a flexible and strong partnership approach to ensure the Assarel project stayed on track and within deadline, being responsible for managing the overall project and detail engineering review.

SPECIAL CONSIDERATIONS AND FEATURES

High rain and snowfalls are normal in the area, resulting in a high amount of solids in the incoming PLS feed. To overcome this, the old cementation cells were modified for use as a PLS pre-treatment process to settle out the solids from the feed solution. The PLS pond was the only facility to remain located outside, despite the temperature of the incoming feed dropping well below 10�C. This allowed the incoming PLS to be steam heated and avoid mixing and phase separation problems later in the solvent extraction process.

Special attention was given to internal air quality to protect both the process operators and the equipment, with all

Cu solvent extraction

Output SEAP December 2012 / 9

SX mixer-settlers, the after-settler, and the loaded organic tank equipped with low, sealed roofs. The electrolytic circuit was fitted with double contact busbars to reduce the number of short-circuits in the EW system and an acid mist capture system to improve air quality in the EW hall and reduce environmental emissions. The electrowinning cells were equipped with hoods and vented to an acid mist scrubber, with fumes from the stripping machine washing chamber also vented to the scrubber.

Another feature, with both environmental and economic benefits, was the recycling of sulphuric acid and copper sulphate washed away from the EW hall air. The chemicals were re-used in the SX process washing stage, eliminating the need for extra acid or water.

THE NEW PLANT LAYOUT AND PROCESS

Throughout the plant flowsheet, process liquids/chemicals such as water, raffinate, filtrate, organic solution, lean and rich electrolyte are gravity recycled back to the system, reducing organic losses, operating costs and environmental impact.

Solvent Extraction – The solution from dump leaching is pumped from the PLS pond to the first of two extraction stages, where copper is extracted from the solution with a selective reagent. Aqueous entrainment is separated from the loaded organic solution, then washed to remove chemically and physically entrained impurities.

The washed loaded organic flows to the stripping stage where copper is transferred to the electrolyte solution. SX plant organic can be treated with bentonite to remove the impurities from the organic phase.

Tankfarm – Rich electrolyte from the stripping stage flows to the after settler, from where it is pumped through electrolyte filters to the electrolyte circulation tank, consisting of two round vertical tanks, joined by interconnecting pipes. Electrolyte additives, guar and cobalt, are dosed to the EW feed electrolyte. Lean electrolyte is pumped back from the circulation tank to solvent extraction through a heat exchanger.

Electrowinning – Circulation electrolyte is pumped into the EW cells where copper from the solution is reduced to metallic copper. Current from the transformer-rectifiers passes through the electrolyte depositing copper at the stainless steel cathode with oxygen being liberated at the anode.

Cathodes are grown in ten electrolytic cells, with each cell containing 32 permanent stainless steel cathodes. The circulating electrolyte’s copper concentration is 38.3g/L and lean electrolyte has 36g/L acid concentration in the electrolyte is 170–190g/L. Design current density is 320A/m2.

FIRST-IN-WORLD TECHNOLOGY

The Assarel mixer-settlers were designed to have stage efficiencies above 95% and very high settling rates. The SX settlers have settling rates from 8.8 to 9.7m3/m2/h, making them the most compact and efficient SX settlers in the world. The settling rate in Assarel is double that of standard industrial practices, so reducing the equipment size by 40% and the organic inventory by 30%.

The Assarel Cu SX process is also the first Cu SX plant where reverse and straight flow mixer-settlers are connected, combining the advantages of the different flow profiles.

Reconstructed cementation cells and PLS tanks

Output SEAP December 2012 / 10

INNOVATIVE THINKING

Design feed solution flow to the Cu SX process is 500m3/h. The PLS feed contains only 0.6g/L of copper. Usually for this concentration range the IX process would have been an option, however, because of the amount of the PLS flow, PLS maximum solids concentration and PLS minimum temperature, the IX process was rejected. To make this size of Cu production and investment possible, Outotec needed to design a special process for SX. The chosen SX configuration was 2E+LOT+1W+1S. Two extraction stages were connected in series to ensure as high as possible extraction efficiency (>92%).

REDUCED CAPEX/OPEX

Apart from Assarel’s highly efficient settling rates (reducing equipment size by 40%, organic inventory by 30%), Outotec reduced capital expenditure with other innovative

solutions. A low O/A-ratio (0.25) gives a high organic phase loading, rejecting impurities. The plant’s capital and operational costs were also reduced with a 75% reduction in the physical size of the washing and stripping mixer-settlers, double contact busbars and the acid mist capture system. Additionally, due to innovative design, the SX copper transfer capacity can be tripled from 2,000t/a to 6,000t/a, without any extra process equipment investments.

RESULTS

Prior to the plant upgrade, process restrictions at Assarel were high solids concentration in the incoming feed (up to 1-2g/L during wet season), low copper concentration in the feed due to dilution (<1g/L)

and a very small copper production capacity (2,000tpa Cu). Results from production capacity are now at 2,000tpa LME grade A copper cathode, with working conditions and operator safety substantially improved.

Innovative thinking resulted in some unique, world first designs being established at the Assarel cathode production facility, enabling substantial reductions in CAPEX and OPEX costs.

The new copper plant at Assarel was commissioned by Outotec in November 2010, on time and on budget, with the first cathode produced in December, less than a month after the plant commissioning began.

First cathode growing cycle

If you would like more information, click here to contact

mark.weatherseed@outotec.com