Treatment and Disposal of Residues From Aluminium Dross Recovery [PDF]

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TREATMENT AND DISPOSAL OF RESIDUES FROM ALUMINIUM DROSS RECOVERY K.E. Lorber Institute for Sustainable Waste Management and Technology (IAE), Montan University Leoben

A-8700 Leoben Tel. +43 (0) 3842 402-5101 iae.unileoben.ac.at

Franz-Josef-Straße 18 Fax +43 (0) 3842 402-5102 [email protected]

Contents 1. INTRODUCTION 1.1 1.2 1.3

Dross Formation & Characterization Metal Recovery from Dross Dross is Hazardous Waste

2. LANDFILLING of FINE DROSS-RESIDUES 2.1 2.2 2.3

Gas-Formation Potential & Gas Migration Site-Investigation Results Groundwater Pollution

3. PYROMETALLURGICAL TREATMENT 3.1 3.2

Salt Cake Leaching & Crystallization Process Calcination & REFINING of OXIDIC RESIDUES

4. CONCLUSIONS DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 2

1. INTRODUCTION

1.1 Dross Formation & Characterization Al-DROSS:

Residue from Al-Industry, formed during REFINING and by AIR OXIDATION of liquid metal during MELTING, SKIMMING, HOLDING & CASTING OPERATIONS ALUMINIUM DROSS: Unwanted Residue Complex Mixture of: Metallic Oxides Nitrides Carbides Sulfides Salts from Fluxing Process (NaCl, KCl, Na3AlF6, etc.) Dirt Impurities Metallic Aluminium Recovery

DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 3

DROSS COMPOSITION COMPOSITION of DROSS

R E

TYPE of DROSS

METALLIC Al [%]

RESIDUAL COMPOUNDS

Untreated DROSS

< 80%

Flatcake & Crumbs

90-70%

Al2O3, Al2O3 * MgO, AlO3 * SiO2, Al2O3 * FeO, etc.

R

Concentrate

70-50%

Y

Coarse Residue

50-20%

Fine Residue

20-5%

C

O V E

DepoTech 2012

Al2O3, AlCl3, NaCl, KCl CaF2, NaF, AlF3, etc. Al2O3, AlN, Al4C3, Al2S3, AlP, etc.

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 4

DROSS FORMATION PROCESS STEPS: Surface Oxidation Oxidized Skin (Al2O3) Cracking Sinking & Floating of Al2O3 Conglomeration of Al2O3 Interspace filling by metallic Al Inside Oxidation of metallic Al Skimming Metallic Al Separation

DEPENDING ON: INPUT MATERIAL (e.g. Type of SCRAP etc.)

TECHNOLOGY and OPERATION applied DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 5

1.2 Metal Recovery from Dross

WASTE-Problem: DepoTech 2012

FINE RESIDUES from Al-Recovery O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 6

CHARACTERIZATION of DROSS OECD-Definition: SKIMMINGS: DROSS:

> 45% METALLIC ALUMINIUM < 45% METALLIC ALUMINIUM

- „WHITE DROSS“: - „BLACK DROSS“:

from PRIMARY SMELTER without SALT COVER from SECONDARY SMELTER (e.g. ROTARY FURNACE) with SALT COVER

ENVIRONMENTAL PROBLEM:

HIGH REACTIVITY (i.e. stron exo thermic reaction) with WATER or HUMIDITY in Air 2Al + 2AlN + Al4C3 + Al2S3 + Al4C3 + 4Al(CN)3 + 2 AlP + 3 H2O

3H2O 3 H 2O 6H2O 3H2O 6N2 6H2O

    + + 

Al2O3 Al2O3 2Al2O3 Al2O3 9C

+ + + +   Al2O3 + 2 H3P

3H2 2NH3 3CH4 3H2S 4Al(CN)3 2Al2O3

(1) (2) (3) (4) + (7)

(5) 12 HCN (6)

PHENOMENA of SURFACE PASSIVATION by Al2O2 – Skin formation DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 7

1.3 DROSS is HAZARDOUS WASTE WASTE PROPERTIES • • • •

H3-A: „Highly flammable“ H 4: „Irritant“ H 5: „Harmfull“ H 13: „Toxic Leachate“ (i.e. Fluoride content)

EC-List of HAZARDOUS WASTES 100308* 100309* 100310* 100315*

Salt slags from secondary smelting. Black drosses from secondary smelting. Waste from treatment of salt slags and black drosses. Skimmings that are flammable or emit, upon contact with water, flammable gases in dangerous quantities 100304* Primary smelting slags and white dross

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O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 8

2. LANDFILLING of FINE DROSS RESIDUES About 15-20 years ago: FINE RESIDUES from Al-RECOVERY Process for Dross were LANDFILLED. ENVIRONMENTAL PROBLEMS: High REACTIVITY of FINE DROSS RESIDUES with WATER or HUMIDITY in Air. OLD LANDFILLS: Insufficient Surface Capping: Gas Migration (e.g. H2, CH4, NH3) Insufficient Bottom Sealing: Groundwater Pollution (e.g. F-, Cl-, NH4+(NO3-), CN-, etc.) by vertical MOLECULAR DIFFUSION DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 9

2.1 Gas Formation Potential & Gas Migration Laboratory Test: over 24 days

Average Gas Formation Potential: 8.4 NmL/kgDM per day

Field Measurements of Soil Gas: Explosive Mixture H2: > 4.2 Vol% CH4: > 7.2 Vol% NH3: > 2.4 Vol% DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 10

2.2 Site-Investigation Results (Case Study)

LANDFILLED DROSS: SITE INVESTIGATION

MIGRATION of TOXIC GASES

DepoTech 2012

SITE INVESTIGATION by EXCAVATION & DRILLING O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 11

Site-Investigation Results (Case Study)

LANDFILLED DROSS: SITE INVESTIGATION by EXCAVATION

COMPACTED WET SURFACE LAYER

FOLLOWING DRY LAYER with „SANDWICH-STRUCTURE“

0.5 – 1.5 m: ON TOP 14.5 – 15.5 m: AT BOTTOM

(Dust like MATERIAL: 1.5m – 14.5m)

DepoTech 2012

1.5 – 5.5 m O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 12

MULTIPLE LAYER DEPTH PROFILE (Case Study)

DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 13

2.3 Groundwater Pollution (Case Study)

GROUND WATER POLLUTION caused by MOLECULAR DIFFUSION TRANSPORT PROCESS. Correlation between GROUND WATER TABLE HEIGHT [m] and CONCENTRATION of POLLUTANT (e.g. Chloride) in GROUNDWATER-PROBE [mg/L].

MODEL PREDICTION

(source: RAUPENSTRAUCH & SCHÖNBERG 2010)

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O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 14

Groundwater Pollution (Case Study)

OBSERVED FIELD MEASUREMENT RESULTS

(source: RAUPENSTRAUCH & SCHÖNBERG 2010)

Observed TEMPERATUR INCREASE with local „HOT-SPOTS“ (EXOTHERMIC REACTION) during high GROUNDWATER TABLES. No Correlation with local PRECIPITATION. Nitrification Phenomena: NH4+ NO3-

DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 15

3. PYROMETALLURGICAL TREATMENT STATE-OF-THE-ART: Melting of FINE DROSS RESIDUES together with Al-SCRAP in a salt cover Rotary Furnace (RF) or Tilting Rotary Furnace (TRF).

Tilting Rotary Furnace in secondary Aluminium Industry Product: Metallic Aluminium Residue: Salt Slag or „Salt Cake“ (i.e. Hazardous Waste EC 100310*) DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 16

3.1 Treatment & Recovery Process for Aluminium Dross and Salt Cake SALT CAKE LEACHING & CRYSTALLIZATION PROCESS followed by CALCINATION of OXIDIC RESIDUES

DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 17

3.2 Calcination & Refining of OXIDIC RESIDUES Oxidic Residue (i.e. Hazardous Waste EC 100310*) can be REFINED by CALCINATION (e.g. 24h – Treatment at 1200 °C) VALUE ADDED PRODUCTS

MATERIALS COMPOSITION … unwanted compounds

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O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 18

4. Conclusions Due to the Properties of Wastes Criteria H3-A, H4, H5 and H13, ALUMINIUM DROSS as well as FINE DROSS RESIDUES are HAZARDOUS WASTES. Al-DROSS shows high reactivity with water and moisture, leading to high GAS FORMATION POTENTIAL and strong LEACHABILITY. Landfilling of Dross nowadays is forbidden, because of H2, CH4, NH3 Migration with soil gas and groundwater pollution by F-, Cl-, NH4+ (respectively NO3-) and CN-. Groundwater Pollution cannot be prevented by surface capping, as the pollution transport process is not percolation (advection)but molecular diffusion. STATE-OF-THE ART is the PYROMETALLURGICAL Treatment of Dross under salt cover in a Rotary Furnace. The remaining „SALT CAKE“ is treated in the „LEACHING & CRYSTALLIZATION-Process“ for recovery of Al-Metal & Salt Flux. By CALCINATION-REFINING, remaining OXIDIC RESIDUES can be converted into value added products. DepoTech 2012

O.Univ.Prof.Dipl.-Ing.Dr.techn. Karl E. Lorber, 20.12.2012, Folie 19