Technologies & Processes | 铝渣回收技术与冶金工艺知识总览

Recovery routes classified by thermal state, reaction control and residue destination

按热态、反应控制方式与残渣去向分类的回收路线

Route Selection: Three Deciding Variables

Routes are not ranked here, because no route is universally superior. Selection turns on three variables:

Variable	Why It Decides
Thermal state at intake	Hot dross permits recovery without external fuel. Once cooled, the metal must be remelted and the energy must come from somewhere — fuel, plasma, or oxidation of the metal itself.
Salt content	Salt-flux melting improves metal yield but generates salt cake, a residue requiring its own treatment chain. Salt-free routes avoid that stream but make different demands on energy and temperature control.
Residue classification	Where the residue is classed as hazardous — as under China’s HW48 codes — the downstream obligation, not the recovery yield, often determines the route.

1. Hot Dross On-Site Recovery

Intervention while the dross is still hot. The objective is to separate metal and arrest oxidation before the thermite reaction consumes the recoverable fraction.

Route	Mechanism	Parameter Basis
Hydraulic dross pressing 液压铝渣压榨	A press head compresses hot dross inside a pan; entrained liquid metal drains through pan apertures into a sow mould below. The tooling also acts as a heat sink, and compression itself restricts oxygen access.	Force: nominal ~100 tonnes (≈1,000 kN) on widely installed units — not the 150–500 t range sometimes quoted Cycle: 3–5 min (compact) to 6–8 min per pan Recovery: in-house drain 5–25%; secondary recovery 40–70%
Mechanical agitation 机械搅拌炒灰	Open or semi-sealed pans in which the hot mass is stirred, promoting coalescence and drainage of metal. Lower capital cost; atmosphere control is weaker than in pressing.	Capital and recovery figures are installation-specific; no verified generic range is published by this institute
Inert Gas Dross Cooling (IGDC) 惰性气体冷却	Hot dross loaded into a partitioned pan of high thermal mass; a hood closes over it and argon is introduced to displace oxygen, arresting the exothermic reaction.	Basis: US 4,842,255 (Alcan International). Published report — 1 t cooled below 400 °C in under 4 h; ~60% improvement in recovered aluminium versus dross room cooling. Patent record →

Pressing and inert-gas cooling are sometimes presented as competing. They address different variables: pressing extracts metal mechanically, inert gas preserves it chemically. Plants run both.

Mainstream technologies compared →

2. Cold Dross & Residue Processing

Treatment of cooled dross, fine skimmings and black dross — including material received from external sources. Here the metal must be remelted, and the energy source becomes the defining choice.

2.1 Salt-Flux Rotary Furnace (TRF)

The conventional route. Dross is charged to a tilting rotary furnace under a molten salt cover.

Parameter	Value / Note
Salt system	NaCl–KCl base, typically 70:30 by weight in Europe and 50:50 molar in North America, with fluoride additions — commonly CaF₂ at 2–5 wt% or cryolite
Eutectic	Liquidus minimum of the NaCl–KCl system at 645 °C (≈44 wt% NaCl) — below the melting point of aluminium, so the flux is molten and active from first contact. Pure NaCl melts at 801 °C
Function of fluoride	Fluoride ions act as surface-active species at the metal–oxide interface, inducing oxide phase modification and cracking; this strips the oxide skin so droplets can coalesce. Reported metal yield response to CaF₂ is non-linear, with an inflection near 0.5 wt%
Operating window	Rotary furnace processing is documented in the 700–850 °C range; patent literature cites 750–850 °C as preferred. Above ~800 °C fine aluminium reacts rapidly with oxygen and then nitrogen
Residue	Salt cake — requiring the treatment chain described in section 3

TRF & oxy-fuel combustion →

2.2 Plasma Arc Salt-Free Melting

Developed explicitly to remove the salt cake problem. Documented installations:

Installation	Record
Alcan, Jonquière, Quebec Guillaume-Tremblay Works	Two plasma rotary furnaces; annual capacity cited as 14,000–15,000 t of dross. Non-transferred plasma torch operated with air. Dross charged without preparation; products cooled to 400 °C under argon to limit Al₂O₃ and AlN formation. Aluminium recovery 80–90% (relative to metallic Al input); cited elsewhere as 85–95%. Development team: Lavoie, Dubé, Huni, Stevens — matching the inventors of US 5,421,850
Plasma Processing Corp., Ravenswood, WV	Annual capacity 40,000 t of aluminium dross; non-transferred-arc torches operated with oxygen — which lowers AlN content while promoting exothermic Al₂O₃ formation, reducing electrical power demand
Pilot data 1 MW torch, ~3 t/h	Electrical input estimated at ≈844 kWh/t for nitrogen plasma and ≈475 kWh/t for air plasma. Torch gas heated above 5,000 °C; furnace held at positive pressure to prevent air infiltration

Practical note: a rotary salt-free furnace was subsequently commissioned at Voerde, Germany, using an oxy-fuel burner instead of a plasma torch. Published assessment states that plasma use in dross processing depends on local energy cost relations. Plasma is therefore one implementation of salt-free melting, not its definition.

3. Residue Valorization

What remains after metal recovery — secondary dross, salt cake, and collected dust — carries the regulatory burden. Under China’s hazardous waste catalogue this material falls under HW48:

Code	Waste	Hazard
321-024-48	Primary aluminium dross; salt slag and secondary dross from recovery	R, T
321-026-48	Secondary aluminium and fabrication dross; salt slag and secondary dross	R
321-034-48	Dust from flue-gas treatment of dross recovery and remelting	T, R

3.1 The Governing Reaction: AlN Hydrolysis

The defining hazard of secondary dross is aluminium nitride. On contact with water:

AlN + 3H₂O → Al(OH)₃ + NH₃↑

Each mole of AlN reacts with three moles of water to yield aluminium hydroxide and ammonia. Published thermodynamic assessment gives the Gibbs free energy of this reaction at roughly −218 to −195 kJ/mol across 303–373 K — spontaneous under standard conditions, and exothermic. Hydrolysis product depends on temperature: above 351 K the amorphous AlOOH form is favoured, below it Al(OH)₃.

Practical consequence: ammonia release is the reason storage rules for these wastes require sealed containers, dry conditions and ammonia capture. It is also why any wet route must manage the gas stream, not merely the liquor.

3.2 Treatment Routes

Route	Mechanism	Output / Constraint
Hydrometallurgical leaching 湿法脱氮脱盐	Water or aqueous media leach soluble chlorides and drive AlN hydrolysis; ammonia is captured and the liquor is processed to recover salts and aluminium-bearing products	Recovers flux salts for reuse and yields aluminium compounds. Documented drawback: salt recovery requires evaporative concentration, which is energy-intensive — published minimum around 0.64 kWh per kg of water for single-stage evaporation
Thermal calcination 高温煅烧	Calcination in the 800–1,300 °C range, typically with calcium-based fluoride fixation agents added. Reported outcomes: AlN conversion ≥98%, conversion of fluorides to stable CaF₂, and conversion of low-reactivity alumina into an active resource	Calcium aluminate (for steelmaking desulphurisation, water treatment) and refractory or construction material feedstock. Product specifications exist: YB/T 4265, GB/T 201, GB/T 29341
Cement kiln co-processing 水泥窑协同处置	Use of aluminium-bearing residue as a raw feed component in cement production	Identified in official responses as an applied route; subject to the co-processing standard HJ 662

Residue valorization routes in full →

Verification Status

• Traced — attributable to a patent specification, peer-reviewed paper, association dataset or official regulatory document.
• Installation-specific — varies by site and feed composition; reported as a range with the source noted.
• Unverified — cannot be traced to a primary source; marked inline rather than presented as established.

Recovery percentages quoted without a stated basis — whether relative to metallic aluminium input, to total dross mass, or to a named installation — are treated as unverified on this site. The distinction materially changes the number.

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中文摘要 · 铝渣回收技术与冶金工艺总览

基本盘：铝渣是氧化物与夹带金属铝的混合物，报道的金属含量区间为 30–70%（质量分数），原铝扒渣可达 80%；渣量约占熔体体积的 1–8%。

核心约束是时间。专利文献给出铝的氧化热为 8.7 kWh/kg 金属——失控的热渣会自行放热：细粒自由金属氧化释放能量，推动更多金属氧化，即”铝热”反应。这正是热渣在空气中不会自行冷却的原因，也是所有路线本质上在争夺的：谁赢得与氧化的赛跑。

路线选择的三个决定变量：入料热态（热渣可无外加燃料回收；一旦冷却，重熔能量必须由燃料、等离子或金属自身氧化提供）、含盐与否（盐熔提高收率但生成盐渣这一需独立处理链的残渣；无盐路线避开该物料流，但对能源与温控提出不同要求）、残渣归类（在中国 HW48 下，往往是下游义务而非回收率决定路线）。本站不对路线排名——没有普适最优解。

1. 现场热渣回收。液压压榨：压头在锅内压缩热渣，夹带铝液经开孔流入下方锭模，工具同时充当吸热体并限制氧气进入。广布机型标称压力约 100 吨（≈1000 kN）——并非坊间常引的 150–500 吨；循环 3–5 分钟（小型）至 6–8 分钟/锅；厂内沥铝率 5–25%，二次回收率 40–70%。机械搅拌炒灰：敞口或半密封盘中搅拌促聚并沥出金属，资本投入较低但气氛控制弱于压榨。惰性气体冷却（IGDC）：依据 US 4,842,255（Alcan International），公开报告为 1 吨料 4 小时内冷至 400°C 以下，相对渣房冷却回收铝提升约 60%。压榨与惰性冷却并非互斥——压榨是机械取金属，惰性气体是化学保金属，工厂常两者并用。

2. 冷渣与残渣深加工。加盐回转炉（TRF）：盐系为 NaCl–KCl 基体，欧洲常用 70:30 质量比、北美常用 50:50 摩尔比，并添加氟化物（CaF₂ 2–5% 或冰晶石）。NaCl–KCl 系液相线最低点为 645°C（约 44% NaCl 质量分数），低于铝熔点，故熔剂自接触熔体起即为液态活性状态；纯 NaCl 熔点 801°C。氟离子的作用是在金属—氧化物界面充当表面活性组分，诱发氧化相变与开裂从而剥离氧化膜、使液滴聚并；CaF₂ 对金属收率的影响呈非线性，拐点约在 0.5%（质量分数）。回转炉处理区间为 700–850°C，专利文献以 750–850°C 为优选；超过约 800°C 细铝先与氧、再与氮剧烈反应。产物残渣为需独立处理链的盐饼。

等离子无盐熔炼为消除盐饼问题而开发。Alcan 加拿大 Jonquière（Guillaume-Tremblay 厂）：两台等离子回转炉，年处理14,000–15,000 吨铝渣，非转移型等离子炬以空气运行，物料不预处理，产物在氩气下冷却至 400°C 以抑制 Al₂O₃ 与 AlN 生成，铝回收率 80–90%（相对金属铝投入），另有 85–95% 的报道口径；研发团队 Lavoie、Dubé、Huni、Stevens，与 US 5,421,850 发明人一致。Plasma Processing Corp.（西弗吉尼亚 Ravenswood）：年处理 40,000 吨，非转移弧炬以纯氧运行，可降低 AlN 含量并促进放热 Al₂O₃ 生成，从而减少电耗。中试数据：1 MW 炬、约 3 t/h，电耗约 844 kWh/t（氮等离子）与 475 kWh/t（空气等离子），炬内气体加热至 5000°C 以上，炉内维持正压防止空气渗入。

实践提示：德国 Voerde 后续投产的无盐回转炉采用富氧燃烧器而非等离子炬；公开评估指出等离子在铝渣处理中的应用取决于当地能源成本关系。因此等离子只是无盐熔炼的一种实现，而非其定义。

3. 残渣资源化。金属回收后剩余的二次铝灰、盐饼与收尘粉尘承担监管义务，在中国归入 HW48：321-024-48（原铝铝灰渣及回收过程盐渣、二次铝灰，R/T）、321-026-48（再生铝及加工铝灰渣及其盐渣、二次铝灰，R）、321-034-48（铝灰热回收与再生烟气除尘粉尘，T/R）。

决定性反应——AlN 水解：AlN + 3H₂O → Al(OH)₃ + NH₃↑。每摩尔 AlN 与三摩尔水反应生成氢氧化铝并释放氨；公开热力学评估给出该反应在 303–373 K 区间的吉布斯自由能约为 −218 至 −195 kJ/mol，标准条件下自发且放热。水解产物随温度而变：高于 351 K 倾向生成无定型 AlOOH，低于则生成 Al(OH)₃。实际后果是：氨释放正是这类废物贮存要求密闭容器、干燥条件与氨气收集的原因，也是湿法路线必须管理气相而非仅处理液相的原因。

处理路线：湿法浸出——水或水溶液浸出可溶氯化物并推动 AlN 水解，捕集氨并回收盐与含铝产品；已载明的缺点是盐回收需蒸发浓缩，能耗高，单级蒸发公开最低值约 0.64 kWh/kg 水。高温煅烧——800–1,300°C 焙烧，通常配入钙基固氟剂；报道效果为 AlN 转化率 ≥98%、氟化物转化为稳定 CaF₂、低活性氧化铝转化为高活性资源；产品为铝酸钙（炼钢脱硫剂、水处理剂）及耐火/建材原料，对应标准 YB/T 4265、GB/T 201、GB/T 29341。水泥窑协同处置——作为水泥生料组分利用，为官方答复中确认的已应用路线，受 HJ 662 规范约束。

核验状态：可追溯（专利说明书、同行评审论文、协会数据集或官方法规文件）、装置特定（随现场与入料成分变化，注明来源的区间）、未证实（无法追溯一手来源，随文标注）。凡未说明基准的回收率——是相对金属铝投入、相对总渣量，还是相对具名装置——本站一律视为未证实，因为基准不同会实质改变数值。