Oxidation of Trivalent Arsenic to Pentavalent Arsenic by Means of a BDD Electrode and Subsequent Precipitation as Scorodite

At a Glance

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

Technical Documentation & Analysis: High-Concentration Arsenic Oxidation via BDD Electrodes

This document analyzes the research on electrochemical oxidation of trivalent arsenic (As(III)) using Boron-Doped Diamond (BDD) electrodes, focusing on the material requirements and economic advantages relevant to 6CCVD’s advanced MPCVD diamond solutions.

Executive Summary

The research validates Boron-Doped Diamond (BDD) electrodes as a superior, cost-effective alternative to hydrogen peroxide (H₂O₂) for oxidizing highly concentrated arsenic effluent from copper production.

High Concentration Capability: BDD successfully oxidized As(III) concentrations up to 20 g/L, simulating industrial gas scrubber solutions, a range where traditional methods struggle.
High Efficiency: Oxidation efficiencies between 91% and 94% were achieved at high arsenic concentrations (17-17.5 g/L) in acidic (sulfuric acid) media.
Stable Precipitation: The resulting pentavalent arsenic (As(V)) was effectively precipitated as highly stable, crystalline Scorodite (FeAsO₄·2H₂O) under controlled temperature and pH conditions.
Economic Advantage: Electrochemical oxidation via BDD electrodes is projected to cost approximately USD 510 per ton of arsenic, representing a 31% saving compared to the H₂O₂ method (USD 740/ton As).
Scale-Up Requirement: Industrial implementation requires large-area BDD electrodes (estimated 580 m² for 5900 t/a conversion), necessitating specialized, large-scale MPCVD manufacturing capabilities.
Material Focus: The success relies on robust, thick BDD layers on conductive substrates (e.g., Niobium) capable of maintaining high current density (100 mA/cm²) and long operational lifetimes (estimated 10 years).

Technical Specifications

The following hard data points were extracted from the experimental results and economic analysis:

Parameter	Value	Unit	Context
Target As(III) Concentration	17.5	g/L	Simulated industrial effluent (acidic route)
Oxidation Efficiency	91 to 94	%	Achieved at high As concentration
Experimental Electrode Area	40	cm²	BDD Anode used in lab setup
Experimental Current Density (J)	50	mA/cm²	Used in 40 cm² experiments
Optimal Current Density (J)	100	mA/cm²	Manufacturer recommended for BDD
Diamond Layer Thickness	≥12	µm	Minimum thickness used on Niobium carrier
Oxidation Time (200 mL, 17.5 g/L)	80	min	Time to achieve 100% oxidation
Operating Voltage (Average)	5	V	Used for OPEX calculation
Projected OPEX (BDD)	510	USD/ton As	Includes KPEX amortization (10-year lifetime)
Projected OPEX (H₂O₂)	740	USD/ton As	Includes 50% surplus and transport costs
Required Industrial Electrode Area	580	m²	Calculated for 5900 tons/year arsenic conversion
Scorodite Precipitation Temp.	~90	°C	Required for crystalline product
Scorodite Precipitation pH	~1	N/A	Required for crystalline product

Key Methodologies

The core methodology involves high-current electrochemical oxidation using BDD electrodes, followed by controlled precipitation.

Electrode Configuration: A Niobium-backed BDD anode (40 cm² area, ≥12 µm diamond thickness) was paired with a stainless steel cathode, separated by a fixed distance of 5 mm.
Solution Preparation (Acidic Route): Arsenic oxide (As₂O₃) was dissolved in 2-molar sulfuric acid (H₂SO₄) at 85 °C to achieve high concentrations (up to 20 g/L As(III)), accurately simulating industrial gas scrubber conditions.
Electrochemical Oxidation: Experiments were conducted at room temperature under continuous stirring, applying a constant current of 2 A, resulting in an experimental current density of 50 mA/cm².
Interference Testing: Model solutions containing common interfering ions (Fe²⁺, Cu²⁺, Sb³⁺) were tested simultaneously to assess their impact on oxidation kinetics and cathode passivation.
Scorodite Precipitation: The oxidized As(V) solution was adjusted to approximately 90 °C and pH ~1. Ferric sulfate (Fe³⁺) was added stoichiometrically, and the reaction was initiated using ground natural scorodite seed crystals (1.1 g) to ensure crystalline product formation.
Verification: The precipitated solid was analyzed using X-ray Diffraction (XRD) to confirm the formation of crystalline scorodite (FeAsO₄·2H₂O).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced BDD materials required to scale this highly efficient arsenic remediation technology from laboratory proof-of-concept to industrial implementation.

Applicable Materials

To replicate and extend this high-concentration, high-current density research, 6CCVD recommends the following materials:

6CCVD Material	Key Specification	Application Relevance
Heavy Boron-Doped Diamond (BDD)	High conductivity, robust thickness (0.1 µm - 500 µm)	Essential for generating hydroxyl radicals (indirect oxidation) and surviving highly corrosive, acidic (H₂SO₄) environments over a 10-year projected lifetime.
Custom Substrates	Niobium, Titanium, or other conductive carriers	BDD films can be deposited onto custom carrier materials, ensuring optimal mechanical stability and electrical contact for large-area anodes.
Polycrystalline Diamond (PCD) Plates	Plates up to 125 mm diameter	While SCD/BDD is preferred for the anode, 6CCVD can supply large-area PCD substrates for testing alternative electrode designs or support structures.

Customization Potential

The transition from the 40 cm² lab electrode to the required 580 m² industrial scale demands specialized manufacturing capabilities that 6CCVD provides:

Large-Area BDD Manufacturing: 6CCVD offers BDD plates and wafers up to 125 mm in diameter/side length, facilitating the assembly of the large electrode modules required for industrial scale-up.
Thickness Optimization: The paper used a ≥12 µm layer. 6CCVD can supply BDD films up to 500 µm thick, offering maximum durability and extended operational lifetime, crucial for minimizing KPEX costs over a 10-year period.
Custom Dimensions and Shaping: We provide precision laser cutting and shaping services to create custom electrode geometries, which may be necessary to implement the proposed continuous flow design (using different electrode sections) to mitigate cathode passivation issues caused by interfering ions (Fe, Cu, Sb).
Metalization Services: Although the BDD anode is the primary focus, 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) for optimizing electrical contacts, current distribution, and potentially developing novel cathode materials to prevent the formation of the passivating residue observed in the experiments.

Engineering Support

The research highlights two critical engineering challenges for scale-up:

Cathode Passivation: The formation of a brown-black residue containing As, Cu, Sb, and Fe on the steel cathode significantly reduced oxidation efficiency after 60 minutes.
Electrode Lifetime: The economic model relies on a 10-year BDD electrode lifetime in strong sulfuric acid.

6CCVD’s in-house PhD team specializes in diamond material science and electrochemistry. We offer consultation services to assist engineers and scientists in:

Material Selection: Optimizing BDD doping levels and thickness for maximum current density (100 mA/cm²) and longevity in highly acidic arsenic solutions.
Electrode Design: Advising on alternative cathode materials or electrode configurations to prevent or manage the deposition of interfering ions during continuous operation for large-scale arsenic remediation projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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

Original Source

DOI: https://doi.org/10.3390/su15119030

References

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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]