1. Introduction

Antimony, as an important non-ferrous metal, is widely used in flame retardants, alloys, semiconductors and other fields. However, antimony ores in nature often coexist with arsenic, resulting in high arsenic content in crude antimony that significantly affects the performance and applications of antimony products. This article systematically introduces various methods for arsenic removal in crude antimony purification, including pyrometallurgical refining, hydrometallurgical refining, and electrolytic refining, detailing their principles, process flows, operating conditions, and advantages/disadvantages.

2. Pyrometallurgical Refining for Arsenic Removal

2.1 Alkaline Refining Method

2.1.1 Principle

The alkaline refining method removes arsenic based on the reaction between arsenic and alkali metal compounds to form arsenates. Main reaction equations:
2As + 3Na₂CO₃ → 2Na₃AsO₃ + 3CO↑
4As + 5O₂ + 6Na₂CO₃ → 4Na₃AsO₄ + 6CO₂↑

2.1.2 Process Flow

1. Raw material preparation: Crush crude antimony into 5-10mm particles and mix with soda ash (Na₂CO₃) at a mass ratio of 10:1
2. Smelting: Heat in a reverberatory furnace to 850-950°C, hold for 2-3 hours
3. Oxidation: Introduce compressed air (pressure 0.2-0.3MPa), flow rate 2-3m³/(h·t)
4. Slag formation: Add appropriate amount of saltpeter (NaNO₃) as oxidant, dosage 3-5% of antimony weight
5. Slag removal: After settling for 30 minutes, remove surface slag
6. Repeat operation: Repeat the above process 2-3 times

2.1.3 Process Parameter Control

• Temperature control: Optimal temperature 900±20°C
• Alkali dosage: Adjust according to arsenic content, typically 8-12% of antimony weight
• Oxidation time: 1-1.5 hours per oxidation cycle

2.1.4 Arsenic Removal Efficiency

Can reduce arsenic content from 2-5% to 0.1-0.3%

2.2 Oxidative Volatilization Method

2.2.1 Principle

Utilizes the characteristic that arsenic oxide (As₂O₃) is more volatile than antimony oxide. As₂O₃ volatilizes at only 193°C, while Sb₂O₃ requires 656°C.

2.2.2 Process Flow

1. Oxidative smelting: Heat in a rotary kiln to 600-650°C with air introduction
2. Flue gas treatment: Condense and recover volatilized As₂O₃
3. Reduction smelting: Reduce remaining material at 1200°C with coke
4. Refining: Add small amount of soda ash for further purification

2.2.3 Key Parameters

• Oxygen concentration: 21-28%
• Residence time: 4-6 hours
• Kiln rotation speed: 0.5-1r/min

3. Hydrometallurgical Refining for Arsenic Removal

3.1 Alkali Sulfide Leaching Method

3.1.1 Principle

Utilizes the characteristic that arsenic sulfide has higher solubility in alkali sulfide solutions than antimony sulfide. Main reaction:
As₂S₃ + 3Na₂S → 2Na₃AsS₃
Sb₂S₃ + Na₂S → Insoluble

3.1.2 Process Flow

1. Sulfidation: Mix crude antimony powder with sulfur at 1:0.3 mass ratio, sulfidize at 500°C for 1 hour
2. Leaching: Use 2mol/L Na₂S solution, liquid-solid ratio 5:1, stir at 80°C for 2 hours
3. Filtration: Filter with filter press, residue is low-arsenic antimony concentrate
4. Regeneration: Introduce H₂S into filtrate to regenerate Na₂S

3.1.3 Process Conditions

• Na₂S concentration: 1.5-2.5mol/L
• Leaching pH: 12-13
• Leaching efficiency: As>90%, Sb loss<5%

3.2 Acidic Oxidative Leaching Method

3.2.1 Principle

Utilizes arsenic’s easier oxidation in acidic conditions, using oxidants like FeCl₃ or H₂O₂ for selective dissolution.

3.2.2 Process Flow

1. Leaching: In 1.5mol/L HCl solution, add 0.5mol/L FeCl₃, liquid-solid ratio 8:1
2. Potential control: Maintain oxidation potential at 400-450mV (vs.SHE)
3. Solid-liquid separation: Vacuum filtration, send filtrate to arsenic recovery
4. Washing: Wash filter residue 3 times with dilute hydrochloric acid

4. Electrolytic Refining Method

4.1 Principle

Utilizes the difference in deposition potentials between antimony (+0.212V) and arsenic (+0.234V).

4.2 Process Flow

1. Anode preparation: Cast crude antimony into 400×600×20mm anode plates
2. Electrolyte composition: Sb³⁺ 80g/L, HCl 120g/L, additive (gelatin) 0.5g/L
3. Electrolysis conditions:
   • Current density: 120-150A/m²
   • Cell voltage: 0.4-0.6V
   • Temperature: 30-35°C
   • Electrode distance: 100mm
4. Cycle: Remove from cell every 7-10 days

4.3 Technical Indicators

• Cathode antimony purity: ≥99.85%
• Arsenic removal rate: >95%
• Current efficiency: 85-90%

5. Emerging Arsenic Removal Technologies

5.1 Vacuum Distillation

Under 0.1-10Pa vacuum, utilizes vapor pressure difference (As: 133Pa at 550°C, Sb requires 1000°C).

5.2 Plasma Oxidation

Uses low-temperature plasma (5000-10000K) for selective arsenic oxidation, short processing time (10-30min), low energy consumption.

6. Process Comparison and Selection Recommendations

Selection recommendations:

• High-arsenic feed (As>3%): Prefer alkali sulfide leaching
• Medium arsenic (0.5-3%): Alkaline refining or electrolysis
• Low-arsenic high-purity requirements: Electrolytic refining recommended

7. Conclusion

Arsenic removal from crude antimony requires comprehensive consideration of raw material characteristics, product requirements, and economics. Traditional pyrometallurgical methods have large capacity but significant environmental pressure; hydrometallurgical methods have less pollution but longer processes; electrolytic methods produce high purity but consume more energy. Future development directions include:

1. Developing efficient composite additives
2. Optimizing multi-stage combined processes
3. Improving arsenic resource utilization
4. Reducing energy consumption and pollution emissions