Oxidation of Trivalent Arsenic to Pentavalent Arsenic by Means of a BDD Electrode and Subsequent Precipitation as Scorodite
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-06-02 |
| Journal | Sustainability |
| Authors | Anna-Lisa Bachmann, Gert Homm, Anke Weidenkaff |
| Institutions | Fraunhofer Research Institution for Materials Recycling and Resource Strategies IWKS |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research validates Boron-Doped Diamond (BDD) electrochemical oxidation as a superior, cost-effective method for treating high-concentration trivalent arsenic (As(III)) effluent from copper production, replacing the expensive hydrogen peroxide (H2O2) method.
- Core Achievement: Demonstrated complete oxidation of 17.5 g/L As(III) to As(V) in a pure acidic solution within 80 minutes using a 40 cm2 BDD electrode at 50 mA/cm2.
- Economic Advantage: BDD oxidation is significantly cheaper, costing approximately USD 510 per ton of arsenic (including KPEX for a 10-year electrode lifetime), compared to USD 740 per ton for H2O2 (including transport and 50% surplus).
- High Efficiency: The electrochemical process showed an efficiency of 91-94% relative to Faradayâs law calculations for high arsenic concentrations.
- Stable Disposal: The resulting As(V) was successfully precipitated as highly crystalline Scorodite (Fe[AsO4]·2H2O) under controlled acidic (pH ~1) and high-temperature (near 100 °C) conditions using seed crystals.
- Interference Challenge: The presence of interfering ions (Cu2+, Sb3+) in model solutions caused the formation of a passivating layer on the stainless steel cathode, preventing 100% oxidation completion and requiring further investigation into continuous process design or alternative cathode materials.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target As Concentration (Input) | 18-20 | g/L As(III) | Industrial gas scrubber effluent |
| BDD Electrode Area (Anode) | 40 | cm2 | Standard laboratory setup |
| BDD Layer Thickness | â„12 | ”m | Minimum specified by manufacturer |
| Cathode Material | Stainless Steel | N/A | Used for most experiments |
| Applied Current (I) | 2 | A | Constant current used |
| Experimental Current Density (J) | 50 | mA/cm2 | Used in 40 cm2 experiments |
| Recommended Max Current Density | 100 | mA/cm2 | Manufacturer optimum |
| Oxidation Time (17.5 g/L Pure As) | 80 | min | Time for 100% conversion (200 mL volume) |
| Electrochemical Efficiency | 91-94 | % | Efficiency relative to Faraday calculation |
| Assumed BDD Electrode Lifetime | 10 | years | Based on strong H2SO4 correspondence |
| Estimated Industrial BDD Area | 580 | m2 | Required for 580 kA current draw |
| Estimated Annual As Conversion | 5900 | t/a | Based on 580 m2 area and 90% utilization |
| BDD OPEX Cost (Electricity) | 440 | USD/t As | Based on 3870 kWh/t As @ 0.113 USD/kWh |
| BDD Total Cost (OPEX + KPEX) | 510 | USD/t As | Total cost including 10-year electrode amortization |
| H2O2 Total Cost (50% Surplus) | 740 | USD/t As | Includes chemical cost and transport |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure focused on simulating industrial acidic arsenic effluent and testing the BDD electrode performance under high concentration and interference conditions.
- Acidic Solution Preparation: Arsenic oxide (As2O3) was dissolved in 2 M sulfuric acid (H2SO4) at 85 °C to achieve concentrations up to 20 g/L As(III), mimicking gas scrubber liquor.
- Electrochemical Cell Setup: A two-electrode cell was used, featuring a Niobium-backed BDD anode (40 cm2) and a stainless steel cathode, separated by 5 mm.
- Oxidation Process: Experiments were run at room temperature with continuous stirring, applying a constant current of 2 A (50 mA/cm2).
- Interference Testing: Model solutions were spiked with relevant metal ions (100 mg/L Fe2+, 700 mg/L Cu2+, 280 mg/L Sb3+) to assess side reactions and competitive oxidation/reduction effects.
- Analytical Monitoring: As(III) and As(V) concentrations were differentiated photometrically, while total arsenic and interfering ion concentrations were tracked using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).
- Scorodite Precipitation: Post-oxidation, ferric sulfate was added (molar equivalent to As(V)). The solution pH was carefully adjusted to ~1.0 near 100 °C, and precipitation was initiated using ground natural scorodite seed crystals (1.1 g).
- Solid Analysis: The precipitated solid was analyzed via X-ray Diffraction (XRD) to confirm the formation of crystalline scorodite (Fe[AsO4]·2H2O).
Commercial Applications
Section titled âCommercial ApplicationsâThe BDD electrochemical oxidation method is highly relevant for industries requiring efficient and stable immobilization of toxic heavy metals, particularly arsenic.
- Mining and Metallurgy (Copper/Gold): Direct application for treating high-volume, high-concentration acidic arsenic effluent generated during the processing of sulfide ores (e.g., chalcopyrite, arsenopyrite) via roasting or smelting gas scrubbing.
- Hazardous Waste Management: Provides a cost-effective and reliable method for converting highly mobile As(III) into stable As(V), enabling precipitation as crystalline scorodite for permanent, environmentally compliant disposal.
- Industrial Water Treatment: Applicable to any industrial process generating acidic wastewater contaminated with high levels of arsenic, offering independence from the volatile global hydrogen peroxide market.
- Electrochemical Reactor Design: The findings necessitate the development of optimized continuous flow electrochemical reactors to mitigate cathode passivation caused by copper and antimony deposition, ensuring sustained 100% oxidation efficiency in complex industrial liquors.
- BDD Electrode Manufacturing: Drives demand for large-scale, cost-reduced BDD electrode production (KPEX target price of USD 7000/m2) to support industrial-scale arsenic remediation facilities.
View Original Abstract
In order to deposit arsenic residues from copper production in a stable way, the trivalent arsenic must first be xidized to arsenic(V). A well-known but quite expensive method for this is oxidation with hydrogen peroxide. In order to enable the oxidation of arsenic on a large scale in the future, a potentially cheaper method has to be found, which offers the possibility of oxidizing extremely high arsenic concentrations. As a novel alternative, electrochemical oxidation using a boron-doped diamond electrode is investigated. Based on previous work, this paper concentrates on the presence of interfering ions during oxidation. Furthermore, it is shown that the electrochemically xidized arsenic(V) can be precipitated as scorodite. Finally, an economic analysis shows the potential financial benefit of oxidation via BDD electrodes compared to hydrogen peroxide.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2012 - Ein Element Schreibt KriminalgeschichteâArsenvergiftungen [Crossref]
- 2019 - Investigation on Flotation Separation of Chalcopyrite from Arsenopyrite with a Novel Collector: N-Butoxycarbonyl-O-Isobutyl Thiocarbamate [Crossref]
- 2016 - Review of arsenic metallurgy: Treatment of arsenical minerals and the immobilization of arsenic [Crossref]
- 2005 - Photocatalytic Oxidation of Arsenic(III): Evidence of Hydroxyl Radicals [Crossref]
- 2018 - Photoelectrocatalytic oxidation of As(III) over hematite photoanodes: A sensible indicator of the presence of highly reactive surface sites [Crossref]