Iontech Paper_1 _Operating Experience From the Buchim Copper Project

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OPERATING EXPERIENCE FROM THE BUCHIM COPPER PROJECT

Todor Angelov, Georgy Savov, Aleksander Tsekov, Ivanka Valchanova

Iontech Engineering LTD, e-mail: [email protected]

Abstract. The Buchim Copper Project has been producing cathode copper since January 2012, using aunique L/IX/SX/EW process, developed by IONTECH .The process recovers copper from sulphide and oxideores and has a number of novel features, that have been integrated into a efficient operations. The original

process design has been refined through a process of continual optimization. Expansion of the existing ionexchange circuit and construction of new facility for treatment of excess drainage waters are in progress.Original operations as well as changes and additions within the plant, which lead to improved plant throughput, recovery and availability, are described.

1. Introduction

Buchim Copper Project comprises a process plant, situated near the village of Buchim and in the southborders of Plachkovitsa Mountain, in Republic of Macedonia. Territorially and administratively the projectbelongs to the municipality of Radovis. It is 95 kilometers away from the Skopje capital, and 170 kilometersfrom the nearest port Thessaloniki (Republic of Greece).The process plant was designed to produce 2400 tpaof cathode copper, however as a result of a planned upgrade, the plant will produce copper cathode at a rateof 2800 tpa. The process plant comprises a leach operation for treatment of the oxide and sulfide ores,together with associated ion exchange, solvent extraction, and electrowinning circuits to separate and recovercopper dissolved from the ores. The project construction was completed in December 2011 and reachedsteady copper production in August 2012 after an extended commissioning, related largely to mechanicalissues. Further changes and additions to a number of the original unit operations within the plant has led to

changes in operational procedures, and recovery, as well as to plant availability levels routinely above 95%.

2. Operations

The Buchim Copper Project includes the following operations: Leaching , Ion Exchange, Solvent Extractionand Electrowining [1]. The main structures at the mine complex are sulfide ore dump, oxide ore heap,pregnant leach solution ponds, plant feed pond, raffinate pond , IX facility and SX/EW plant.(Figure 1)The piping network for dump and heap comprises main lines at ground level and heap supply header pipesalong the heaps, which distribute solution over the surface through a series of dripper lines. All pipingnetworks are HDPE throughout, and are installed manually using special equipment. Leach solutionpercolates down through the ore until it reaches the base of the leach pad. The pad is built on a slight slope

towards a series of solution drains. Oxide ore is leached at application rates between 4 to 6 l/h/m2 ,andsulphide ore between 6 to 9 l/h/m2[2]. In a leach operation, the barren solution from the ion exchange facility(“filtrate”) and solvent extraction plant (“raffinate”) which has a high acid concentration, is fed to the old dumpand oxide heap to produce a “pregnant leach solution” (PLS) suitable for subsequent treatment. The flowregime is regulated according the existing conditions by directing dump and heap effluent stream to individualPLS ponds.

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Figure 1. Buchim Copper Project Flowsheet

From the PLS ponds, solutions are directed to IX facility with a design feed flow rate of approximately 650m3/h. The facility consists of 8 ionexchange columns-4 IONTIX units (Iontech Design )[3]. The obtained IX

regenerant is pumped to plant feed pond, where it is mixed with pregnant leach solution from the leachoperation. Feed solution from the plant feed pond flows into a conventionally designed solvent extraction plant(SX) at a rate between 35-40 m3/h .The SX plant using a 3E x 2S configuration, with “conventional flow”

design. The feed is depleted of copper and returned to leaching as a raffinate solution along with the filtratefrom IX facility, thus forming a very environmentally responsible process by not allowing any discharge into theenvironment. The SX plant recover 90% of the feed copper. The use of a selective copper extractant (LIX 84-I),which operates in a closed circuit inside the plant, allows the copper to be transferred to an electrolyteoperating in a closed circuit with the electrowinning plant. The copper is captured from the strong electrolyte inthe electrowinning plant. The electrowinning process uses a common design. Cells are connected in series toa current transformer rectifier with hydraulic feeding of electrolyte to cells connected in parallel. Scavengercells are not included. The operation uses stainless steel permanent cathodes and Pb/Ca/Sn alloy anodes,assembled in combinations of 25 and 26 units per cell, respectively, contained in a total of 24 cells.The cathodes are removed from the cells and transported for manually stripping by hammer and chisel inorder to separate the deposited copper from the mother plate. The copper cathodes with 99.99% purity are

weighed and banded and the mother plates are rinsed and returned to the cells for the next loading cycle.Themain operational parameters are summarized in Table 1.

Table 1.Buchim Copper Project Main Operational parameters

Leaching Dump Leaching :Leach Area-75000 m2,Solution Application Rate -6-9l/h/ m2;Heap Leaching: Heap Height-60m,Leach Area-77628 m2,SolutionApplication Rate - 4-6 l/h/ m2

PLS Dump PLS:300- 440 m3/h; Heap PLS:160-210m3/h;PLS Grade-0.64gplCu av.

IX resin 64 m

3

(H

+

form);Lewatit TP 207 M+SX feed 35-40 m3/h; 8-10 gpl Cu, 15 gpl H+

Organic 45 m3/h;20 v/v% LIX 84-I diluted in ShellSol D100



Lean Electrolyte 22,5 m3/h,37 gpl Cu ,175 gpl H+

Strong Electrolyte 110 m3/h,49 gpl Cu,160 gpl H+

Electrowinning Permanent Cathodes,280 A/ m2,24 cells,92% Current Efficiency

Productivity 2400 tpa copper cathodes

Product Quality LME (High Purity Grade) Copper

3. Operational Issues

The Buchim Copper Project has been operating continuously since early 2012 and considerable operationaldata has been gained, which has resulted in a better understanding of the process operation of this type ofunique circuit. However, despite the overall very successful operation at the site, some operational issues

were identified. Several process modifications and upgrade works have been undertaken and these will bediscussed below.

3.1 Leaching

3.1.1. Leach Chemistry

After approximately a year of successful leaching operations, the pregnant leach solution chemistry haschanged dramatically-solution copper grade decrease, while acidity and ferric iron concentration increase. Thislead to poor performance of the subsequent ionexchange processes and hence a reduction in the total plantproductivity. The analysis of the leaching operations has shown that this issue was due to improper leachmanagement plan and incorrect application rates. Desirably, application rates for leach solution should be lowenough to provide efficient leaching, but if they are too low or too infrequently applied the ore heaps maypartially dry out, which will stop mineral oxidation and bacterial activity. With copper ores and mine waste, the

rate of copper solubilization usually steadily decreases over the months and years and short applicationsperiods should be followed by rest periods, during which aeration and oxidation of copper minerals willcontinue. An orderly leach management plan, with properly designed application and rest periods andapplication rates are developed and enforced. Compliance with the plan will lead to the restoration of copperand ferric iron grade and the acidity of solution to the optimal levels. The leach management plans both fordump and heap leach operations of the Buchim Copper Project are given below:

Dump Leach Operation

Application Period -3 monthsRest Period-6 months

Application Rate-6-9 l/h/m2

Heap Leach Operation

Application Period -2 monthsRest Period-2 months

Application Rate-4-6 l/h/m2

3.2. Ion Exchange

3.2.1. Ferric Iron

As a result from the improper leach operations ,increased iron concentrations in PLS were encountered andthis lead to some negative impacts on the resin performance .Ferric iron is contributing with copper in uptakeon the resin and this reduces its operating capacity significantly .Besides this, ferric iron can cause damage ofthe resin by precipitation as iron(III) hydroxide(Figure 2), which act as a catalyst for oxidation byoxygen.Therefore to compensate the effects of iron the following modifications in ionexchange process were

undertaken:

• working with high specific flowrates during the exhaustion cycle



• feed solution pH maintaining below 3 (namely 2.6-2.8) to prevent precipitation of iron(III)

• resin regeneration with high specific acid dosage(18-20%)

• resin soaking in acid solution for 1 to 2 hours, before rinse out.

Figure 2. Plant Ion Exchange Resin

3.3. Solvent Extraction

3.3.1Crud

The commissioning of SX/EW plant was followed by a catastrophic collapse in the operation of the SX section.

The phase disengagement times increased and the settlers filled with stable emulsion-crud. The extractionkinetics and the reagent capacity decreased, resulting in a major limitation on the copper transfer to the EWplant. On-site investigation of the cause of the situation determined that it was due to enormous quantities ofsuspended solids in solutions exiting dump leaching .Those effects were eliminated by crud removing from thesettlers with air operated diaphragm pump and by application of a rehabilitation process for the SX organic.The rehabilitation of the organic was achieved using a treatment with acid activated clay. The procedure wasimplemented to the plant organic on a batch basis. Cycle times for the treatment were 1 to 2 hours by using aplate and frame filter to remove the clay, before returning the treated organic to the circuit. The benefit of thistreatment was obvious, as the plant organic returned toward the original extraction capacity, kinetics andphase disengagement times.

3.4. Electrowining

3.4.1. Contaminant Elements Build Up

o Iron

In most SX/EW operations, iron is the primary contaminant element and is transferred into the electrolyte bothby entrainment of pregnant leach solution and by chemical extraction. This build up of iron in electrolyte resultin a loss of current efficiency in the electrowinning process due to the continuous oxidation/reduction of Fe 2+ toFe3+. The method used for controlling the iron concentration in EW section of the Buchim Copper Project isperiodically bleed a portion of the iron-rich, copper-depleted electrolyte from the circuit and replace it with freshelectrolyte. This bleed flow at the Buchim site is 6 cubic meters daily.



o Manganese

Manganese as Mn2+ in the electrowining is not a problem, however the Mn2+ rapidly becomes oxidized toMnO4

- , which is a powerful oxidizing agent and which rapidly degrade both diluents and the extractant in

solvent extraction. This degradation may not initially have a great effect on the maximum copper loading of theorganic, but will reduce extraction kinetics and increase phase disengagement times and entrainment. Thedevelopment of the manganese problem at Buchim Copper Project occurred quickly after commissioning and

was recognized by purple coloration and increased Eh of the electrolyte. The rehabilitation process was donesuccessfully with the addition of ferrous sulfate to the electrolyte and with contacting of the electrolyte with mildsteel and iron wire.

3.4.2 Electrolyte Distribution

The flow distribution of electrolyte within the cells is very important. At the Buchim site this is accomplished byusing a PVC manifolds with 200 distribution holes (100 on each side) at 45 degrees from vertical, placed in the

bottom of the cells.(Figure 3).The use of this type of distribution system increases the velocity of electrolyteacross the face of the cathode plate allowing electrowining operation at higher current densities as well as aproper growth ,orientation and morphology of copper deposit.

Figure 3. Electrolyte Distribution System

3.4.3 Acid Mist Control

Consistent with Buchim’s strong commitment to the environment and its workers, the most modern method forthe control of acid mist generated in the electrowinning cells are employed. The method consists of a hoodlocated over each electrolyte cell that collects the mist and processes it in a countercurrent scrubber with a

water shower. The acid mist is recovered and acid-free air is expelled into the environment. This acid mistcontrol method guarantee a clean and safe environment in the working place, thus protecting the health of

workers and also reducing acid damage to equipment.The summary of operational issues at the Buchim Copper Project and its resolutions are given in Table 2.

Table 2. Operational Issues Summary

Process Оperational issues Resolution

Leaching Changed Leach Chemistry Orderly leach management planIonexchange Ferric Iron Effects Working with high specific flow rates duringexhaustion



Maintain the PLS pH 2.6-2.8

Resin regeneration with high acid concentration

Resin soaking in acid solution

Solvent Extraction Crud Organic treatment with acid activated clay

Electr wining Contaminant Build Up Electrolyte Bleed(for Fe and Mn)Addition of ferrous sulfate to the electrolyte andcontacting of the electrolyte with mild steel andiron wire(for Mn)

Electrolyte Distribution Specially designed PVC manifolds in the EWcells bottom

Acid Mist Control Cells hoods and scrubber

4.Buchim Copper Project Expansion

In 2013 was decided to expand the Buchim Copper Project in order to increase the nominal production up to2800 tpa of copper cathodes and to handle the excess drainage waters. The expansion project will becompleted in late 2013 or early 2014, with the commissioning of the expanded ion exchange circuit and newlyconstructed ionexchange facility for treatment of excess drainage waters. The main components of theexpansion project included:o installation of the four new columns within the existing ionexchange facility

o extractant addition of in SX organic up to 25 v/v%

o revision of contact busbar system in the electrowinning

o construction of new ionexchange facility with two columns for excess drainage waters treatment

5. Conclusions

The Buchim Copper Project provides a valuable case study in all aspects of plant operations for futureimplementations of this type of technology. There are a number of copper deposits worldwide that areamenable to treatment by this type of circuit and the lessons learnt will be valuable in eliminating some of theissues that will inevitably arise during the design and commissioning of plants treating copper oxide and/orsulphide ores.

References

1. Savov G., Angelov T., Tsekov V., Nishkov I., Nikolov N.,.Konzulov G.,. Combined Ion Exchange - SolventExtraction Process for Copper Recovery, In: Proc. of XIV th Balkan Mineral Processing Congress, Tuzla,

Bosna and Herzegovina ,2011,pp.620-6232. Savov G., Angelov T., Tsekov V., Grigorova I., Nishkov I. Heap and Dump Leach Process at the Buchim

Cooper Project – Metallurgical Testwork. In: Proc. of XXII World Mining Congress, Vol. II, Istanbul, Turkey,2011, pp. 271-276.

3. Savov G., Angelov T., Tsekov V., Nishkov I., Development and Applications of Iontech Ion Exchange(Iontix ®) Process, In: Proc. of XXII World Mining Congress, Vol. II, Istanbul, Turkey, 2011,pp.319-322

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Iontech Paper_1 _Operating Experience From the Buchim Copper Project