Extraction of precious metals by high-temperature chlorination of slag
The high-temperature chlorination volatilization technology of slag has unique potential in treating precious metals (such as gold, silver, platinum group metals, etc.), but the process needs to be optimized according to the characteristics of precious metals. The following is a systematic analysis of precious metal recovery:
1. The basic principle of chlorination volatilization of precious metals
Precious metals (Au, Ag, Pt, Pd, etc.) can be converted into volatile chlorides under high-temperature chlorination conditions, but the reaction conditions are relatively harsh:
- Gold (Au): A strong oxidizing atmosphere (such as Cl2+O2) is required to generate AuCl3 (sublimation point 254°C), but it is easy to decompose at high temperature (>300°C).
- Silver (Ag): AgCl (boiling point 1564°C) is generated, but it is easy to melt at high temperature and needs to be combined with a reducing agent (such as C) to promote volatilization.
- Platinum group metals (Pt, Pd, etc.): require high temperature (>800°C) and excess Cl2 to generate PtCl2 and PdCl2, but have low thermal stability and require rapid condensation.
Key reaction formula:
- 2Au + 3Cl2 → 2AuCl3 (requires an oxidizing atmosphere)
- Ag2O + 2Cl2 → 2AgCl + O2
- Pt + 2Cl2 →PtCl4 (easily decomposed at high temperature)
2. Key points of precious metal recovery process
(1) Chlorination agent selection and optimization
- Cl2 gas: most efficient, but requires precise control of oxidizing properties (to avoid AuCl3 decomposition).
- Mixed chlorination agent: Cl2 + air (enhanced oxidizing properties) or Cl2 + CO (reducing properties, promotes AgCl volatilization).
- Solid chlorination agent: such as NaCl + CaO (requires high temperature and carbon assistance, suitable for complex slag).
(2) Temperature and atmosphere control
- Segmented temperature control:
- Low temperature section (200-400°C): Prioritize volatilization of AuCl3 (needs rapid condensation to avoid decomposition).
- Medium and high temperature section (600-900°C): Recover AgCl, PtCl2, etc.
- Atmosphere control:
- Oxidizing atmosphere (Au recovery): Pass O2 or air.
- Reducing atmosphere (Ag recovery): Pass CO or H2 to prevent AgCl from melting.
(3) Slag pretreatment
- Precious metal occurrence state: If encapsulated in silicate, acid leaching or roasting pretreatment is required to release the metal.
- Particle size refinement: Crushed to <100 μm to increase the reaction contact area.
3. Key challenges and solutions
(1) Low efficiency of precious metal volatilization
- Problem: AuCl3 is easy to decompose at high temperature, and AgCl is easy to melt.
- Countermeasures:
- Rapid condensation (quenching device or low temperature trap).
- Adding catalyst (such as CuCl2 to promote Au chlorination).
(2) Difficulty in multi-metal separation
- Step condensation: Utilize the difference in boiling points of different chlorides (such as AuCl3 volatilizes before AgCl).
- Selective chlorination: Control the Cl2 concentration and temperature to preferentially chlorinate precious metals.
(3) Environmental protection and corrosion issues
- Tail gas treatment: NaOH solution absorbs Cl2 and HCl, and activated carbon adsorbs residual precious metal vapor.
- Equipment corrosion protection: Use Hastelloy, graphite lining or ceramic coating reactor.
4. Application scenarios and cases
- Electronic waste: Waste circuit boards contain Au and Ag, which can be extracted by high temperature chlorination (Cl2+air, 800°C).
Technical Support
1) Equipment design
Furnace will be customized to meet your production needing and environmental condition (maximum ambient temperate, humidity, altitude,etc) .
2) Drawings delivery
Technical drawing will be send to the buyer after geting the deposite, so the buyer can build basic contruction before the furnace arrived.
3) Acceptance check before delivery
a. The supply of the inspection equipment complies with the scope of supply and technical specifications in the technical agreement.
b. Check the mechanical actions of the equipment.
4) Installation & debugging & worker training
a. Cooperate with guidance to check the buyer installation work;
b. Internal and electrical wiring connections between equipment;
c. Site commissioning;, according to the actual equipment adjust to the best state;
d. Direct buyer operating personnel to the correct use of operating equipment;
e. Guidance on site security considerations;
f. To guide the buyer maintenance personnel troubleshooting methods;
g. Provide equipment specification;
5) other related equipment for your casting project, such as aluminum ingot maker, mould for mill balls, continous casting machine, ect.
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FAQ
Q1: How is your company's product after-sales service system?
A: We have professional pre-sales and after-sales departments and
can respond to you within 8 hours to resolve any technical issues.
Q2: How about the quality guarantee period?
A: 3-5 years, exclude irrationally operating and consumable parts.
Q3: How about your products quality?
A: CE certification available and twice test before shipping.
Q4: What's your delivery time?
A: Conventional model needs 3 days.35 days for customized products
Q5: Are you a manufacturer or a trading company?
A: We are a factory with 10 years experience in the field.
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