Adrian Rojo

Electrodialytic remediation of copper mine tailings using bipolar electrodes

In this work an electrodialytic remediation (EDR) cell for copper mine tailings with bipolar stainless steel plates was analyzed. The bipolar plates were inserted inside the tailings, dividing it into independent electrochemical cells or sections, in order to increase the copper removal efficiency from mine tailings. The bipolar plates design was tested on acidic copper mine tailings with a fixed: applied electric field, liquid content, initial pH, and remediation time. The laboratory results showed that inserting bipolar plates in EDR cells improves the remediation action, even though the applied electric field is reduced by the electrochemical reactions on the plates. Basically three aspects favor the process: reduction of the ionic migration pathways, increase of the electrode surface, and in-situ generation of protons (H(+)) and hydroxyls (OH(-)). Furthermore, the laboratory results with citric acid addition significantly improve the remediation actions, reaching copper removal of up to nine times better, compared to conventional EDR experiments without any plates or citric acid addition.

Electrodialytic Remediation of Copper Mine Tailings: Sulphuric and Citric Acid Addition

Abstract Decades of mining activities in Chile have generated large amounts of solid waste, which have been deposited in mine tailing impoundments. These impoundments cause concern due to dam failures or natural leaching to groundwater and rivers. This work shows the laboratory results of 11 electrodialytic remediation experiments on copper mine tailings with the addition of sulphuric and citric acid. Comparing this to electrodialytic remediation with watery tailing, both acids enhanced the process. However, with citric acid addition the process was further enhanced because besides the pH decrease a formation of copper citrate complexes occurred. The maximum copper removal reached in the anode side of the remediation cell was 53% with sulphuric acid in 504 h and 35% with citric acid in only 40 h, both experiments at 20 V treating approximately 1.7 kg mine tailing on dry basis.

Electrodialytic remediation of suspended mine tailings

This work shows the laboratory results of nine electrodialytic remediation experiments on copper mine tailings. A newly designed remediation cell, where the solids were kept in suspension by airflow, was tested. The results show that electric current could remove copper from suspended tailings applying 40 mA during 7 days. The liquid-to-solid ratios used were 3, 6 and 9 mL g− 1. With addition of sulfuric acid, the process was enhanced because the pH decreased to either 2 or 4, and copper was therefore dissolved. The maximum copper removal was 80% with addition of sulfuric acid in 7-day experiment at 40 mA, with approximately 137.5 g mine tailings on dry basis. The removal for a static (baseline) experiment only amounted 15% when passing approximately the same amount of charge through 130 g of mine tailings. The use of air bubbling to keep the tailings suspended increased the removal efficiency from 1% to 80% compared to experiments with no stirring but with the same operational conditions. This showed the crucial importance of having the solids in suspension and not settled during the remediation.

Electrodialytic Remediation of Copper Mine Tailing Pulps

Abstract This work compares and evaluates nine electrodialytic laboratory remediation experiments on copper mine tailings. Experiments in the past have applied this method on moist mine tailings, but can also be applied to mine tailing-liquid mixtures. The objective of this work was the treatment of mine tailing pulps. Different parameters were analyzed, such as current density, desorbing agents, and liquid–solid ratio over non-stirred and stirred mine tailings by air suspension. The results showed that the remediation action is improved using mine tailings in pulps. As expected, stirring of the pulp favors the process performance. For 7 days remediation the best results were obtained using air stirring of the pulp, citric acid addition, a liquid/solid ratio (L/S) of 4.0 [mL/g] and a current density of 0.9 [mA/cm2] reaching a 15% removal of the total copper.

Electrokinetic Remediation of Copper Mine Tailings: Evaluating Different Alternatives for the Electric Field

Due to the magnitude of the mining activity in Chile, it becomes necessary to find solutions to mitigate the impact of mining waste on the environment. One method that could be suitable for remediation of mining wastes is the use of electric fields for the removal of metals, the so-called electrochemical remediation: electrokinetic or electrodialytic remediation (EKR or EDR). Especially, metals such as copper, zinc, lead, and arsenic have been removed or concentrated when applying electric fields—and these metals are typically also found in mining waste. The use of this remediation technology will imply the periodic application of the method in order to remove the additional soluble copper that will be generated with time. Therefore, the remediation action for this heterogeneous solid waste is to remove the soluble copper in the tailings and in this way making the final residue more stable.

Behaviour of a copper-AISI 304 stainless steel mixed anode in electrolytic copper refining with periodic current reversal

In the search for suitable materials to be used as anode supports in the periodic current reversal refining process this work covers the study of austenitic AISI 304 stainless steel. Experimental results show that the resistance of this steel to the aggressive action of the refining electrolyte is good at the working temperature of 60°C since no corrosion was detected after 24 h of electrolysis. The periodic polarization of this material results in a progressive passivation which was observed by operating under different initial surface conditions and by detecting remnant anodic currents which gradually decreased with time. For time ratios lower than twenty, a build up of metallic copper deposit on the steel part of the mixed anode occurred whatever the current density used.