Introduction
Materials and methods
Scenario analysis
-
Scenario 1: Current situation. In this scenario, the current situation in which present technologies, input and output data from recycling/end-processing of e-waste has been investigated. Dismantled fractions (plastic, ferrous metal, copper and aluminum) are transported to and recycled at craft villages while PCBs are treated partly for gold and copper recovery. The remaining electronic components (e.g., capacitors, transistors) are exported. Collecting data for this scenario are a challenge as there are very limited number of published articles regarding the informal recycling processes. As stated above in the “Materials and methods”, alternative available sources of information have been used. Data on dust, metal fume, other gases (NO x , SO2, organic compounds) from melting process are not available as no air treatment facilities are installed and missing of input composition analysis. The only available data are some air quality monitoring reports for craft villages from study of Dang [19], MONRE [17] or Dang et al. [16] but those data were not able to interpolate to air emissions from generated pollution sources. As evaluated by Dang et al. [16], air pollution at craft villages has not been reduced but it tends to increase.
-
Scenario 2: Selected BAT. This scenario presents a proposed situation in which, enterprises involved in e-waste end-processing (recycling of metals, PCBs and plastic) are gathered to centralized workshop. Each of them operates separately under selected BAT with BEP by sharing one or more waste treatment facilities. Except for the case of PCB recycling, in which the referred BAT are the current one at Umicore; other selected BAT are based on the following criteria: (1) suitable for recycled materials from e-waste sources; (2) technically upgradable for recyclers/smelters at craft villages; and (3) appropriate for Vietnamese context. The main data sources for selected BATs come from BAT references [20, 21] and data from ecoinvent reports [22‐24]. Air emission from melting operations of smelters is available but depending on input materials (feeding capacity, scrap quality), air treatment technologies, air sucking capacity (volume of sucked air per hours). With appropriate treatment facilities, selected BAT and implemented BEP, emission to air, water and soil supposes to be satisfied environmental standards to be discharged into environment.
Process and data collection
Dismantling of desktop PC
Regrouped materials | Mass percentage (%) |
---|---|
Untradeable | 4.08 |
Ferrous metals | 76.22 |
Plastic | 8.08 |
PCBs | 9.01 |
Copper | 0.80 |
Aluminum + zinca
| 1.80 |
Total | 100.0 |
Energy sources
Power source | 2014 (%) |
---|---|
Hydropower | 40 |
Coal-based thermal | 28 |
Gas turbine | 22 |
Diesel, small-sized hydropower and wind | 5 |
Fuel oil (FO) based thermal | 2 |
Gas-based thermal | 1 |
Imported source | 2 |
Energy type | Unit | Equivalent CO2 emission coefficient | References |
---|---|---|---|
Electricity | kg CO2/kWh | 0.4668 | [31] |
Coal (lump coal, type 4b) | kg CO2/kg | 28.7467 | Calculated from the carbon constituent and oxidation reaction of carbona at the assumption rate of 100% |
Liquefied petroleum gas (LPG) | kg CO2/kg | 2.86 | Calculated from LPG emission factor 12,500 lb/103 gal [28] |
Recycling processes and technologies
PCB treatment
Current selected techniques
Gold recovery | |||
---|---|---|---|
Inputs | Unit | Quantity | Note |
Gold fingers and chips | kg | 4.100 | Calculated with the assumption of overall recovery rate is at 25% and 5.0 g of gold can be extract from each kg of high-gold-contained parts |
Hydrogen peroxide 3% (d = 1 g/ml) | kg | 27.333 | |
Hydrochloric acid (HCl) 20% (d = 1.098 g/ml) | kg | 29.520 | |
Hydrochloric acid (HCl 36%) for aqua regia (d = 1.789 g/ml) | kg | 1.375 | |
Nitric acid (HNO3 68%) for Aqua regia (d = 1.405 g/ml) | kg | 0.360 | |
Water for washing | kg | 20.000 | |
Urea | kg | 0.584 | |
Sodium Bisulfite | kg | 0.058 |
Outputs | Unit | Quantity | Note |
---|---|---|---|
Gold | kg | 0.0205 | |
Wastewater | kg | 80.210 | Contains residue acid, salt solution of metals (e.g. Au3+, Cu2+) and is hazardous waste |
Solid waste | kg | 3.034 | |
Total air emission | kg | 0.066 | |
NO2
| kg | 0.006 | |
Cl2
| kg | 0.018 | Calculated from reaction (5) |
NOCl | kg | 0.016 | Calculated from reaction (5) |
CO2
| kg | 0.003 | Calculated from reaction (6) |
SO2
| kg | 0.024 | Calculated from reaction (7) |
Copper recovery | |||
---|---|---|---|
Inputs | Unit | Quantity | Note |
PCBs | kg | 995.900 | High-gold-contained parts have been separated for gold recovery |
Water | kg | 5000.000 | Water consumption is estimated based on electric pump power (0.37 kW) and its operational time (8 h per day) |
Energy | |||
LPG | MJ | 600.030 | |
Electricity | kWh | 165.983 |
Outputs | Unit | Quantity | Note |
---|---|---|---|
Copper rich material | kg | 284.345 | Mixture of copper and non-copper materials is at the amount of about 42 wt% of total shredded input and overall copper recovery rate is assumed at 95 wt%. Copper content is roundly 241.32 kg |
Solders | kg | 44.019 | Collected and sold |
Transistors, small capacitors | kg | 175.278 | Average and small size components. Exported |
Capacitors and large size components | kg | 99.590 | Second large size components. Exported |
Wastewater | kg | 5,000.000 | Water can be recycled after treatment. As if, wastewater can be reduced to 1000 kg |
Solid waste | kg | 392.667 | Glass fiber and organics, to be landfilled |
Equivalent CO2 air emission | kg | 114.103 | Calculated from data provided in Table 3
|
Selected BAT
Per 1000 kg of PCBs from waste desktop PC | |||||
---|---|---|---|---|---|
Unit | Current operation | Selected BAT | |||
Quantity | Note | Quantity | Note | ||
Inputs | |||||
PCBs | kg | 1000.000 | 1000.000 | ||
Chemicals | kg | 59.231 | |||
Water | kg | 5020.000 | |||
Energy | – | The energy content exceeds energy demand for smelting and refining | |||
Electricity | kWh | 165.983 | |||
LPG | MJ | 600.030 | |||
Recovered metal outputs | |||||
Gold | 0.0205 | 0.078 | |||
Copper rich material | kg | 284.345 | In which, the copper content is 241.257 kg | 242.250 | |
Solder metals | kg | 44.019 | |||
Other metals | kg | – | 62.316 | Other metals include precious metals (Au, Ag, Pd), base and special metals (Ni, Sn, Sb) | |
Total recovered metals | kg | 285.299 | Without non-copper materials in the mixture output from copper recovery (43.088 kg) | 304.654 | |
Other fractions/streams | |||||
Exported components | kg | 274.868 | – | ||
Burned fraction for energy recovery | kg | – | 512.400 | ||
Solid waste | kg | 395.701 | – | ||
Metal in slag and other waste streams | kg | – | 182.945 | Metal in slag is used as construction material and in the concrete industry | |
Copper content in wastewater from gold recovery | kg | 1.05 | Copper salt solution | – |
Ferrous metal recycling
Current technology
Input | Unit | Current technology | Selected BAT | ||
---|---|---|---|---|---|
Quantity | Note | Quantity | Note | ||
Steel scraps | kg | 1000.00 | 1000.00 | ||
Flux (lime/dolomite) | kg | 9.26 | 9.52 | ||
Auxiliary | kg | 9.26 | FeMn80 and FeSi75 | 6.67 | |
Refractory—ceramic powder | kg | 3.70 | 3.81 | ||
Cooling water | kg | 6481.48 | Without water recycling | 380.95 | Added water or lost water by evaporation |
Electricity | kWh | 925.93 | 550.00 |
Output | Unit | Quantity | Note | Quantity | Note |
---|---|---|---|---|---|
Product | kg | 925.93 | 952.38 | ||
Total solid waste | kg | 46.76 | 21.81 | ||
Solid waste—impurities | kg | 11.57 | – | ||
Solid waste—metal slags | kg | 23.15 | 15.00 | ||
Liquid metal scattered during pouring and metal residues from steel billets (recyclable) | kg | 12.04 | – | ||
Refractory waste | kg | 3.70 | 3.81 | ||
Dust collected from air treatment facility | kg | – | 3.00 | ||
Wastewater | kg | 4629.63 | – | ||
Equivalent CO2 emission | kg | 432.27 | Calculated from data provided in Table 3
| 256.77 |
Selected BAT
Plastic recycling
Current technology
Selected BAT
Unit | Current technology | Selected BAT | |||
---|---|---|---|---|---|
Quantity | Note | Quantity | Note | ||
Input | |||||
Plastic scraps | kg | 1000.00 | 1000.00 | ||
Cooling water | kg | 20,280.37 | 14,563.11 | ||
Electricity | kWh | 327.10 | 194.17 | ||
Output | |||||
Product | kg | 934.58 | 970.87 | ||
Total solid waste | kg | 47.66 | 10.68 | ||
Solid waste—impurities | kg | 10.28 | 10.68 | ||
Solid waste—scattered pellets (recycled) | kg | 37.38 | – | ||
Wastewater | kg | 18,411.21 | Without water recycling | – | Cooling water is recycled. Water is lost by evaporation at small volume |
Air emission (dust, smoke) | kg | – | – | ||
Equivalent CO2 emission | kg | 152.71 | Calculated from data provided in Table 3
| 90.65 |
Aluminum recycling
Current technology
Unit | Current technology | Selected BAT | |||
---|---|---|---|---|---|
Quantity | Note | Quantity | Note | ||
Input | |||||
Aluminum scraps | kg | 1000.00 | 1000.00 | ||
Water (for cooling) | kg | 12,378.69 | 282.78 | ||
Water (for surface treatment) | kg | 2063.11 | 2356.49 | ||
NaOH | kg | 8.25 | 8.95 | ||
NaNO3
| kg | 8.25 | 9.43 | ||
Chromic acid | kg | 2.06 | 0.71 | ||
Sulfuric acid | kg | 0.76 | 0.87 | ||
Electricity | kWh | 31.36 | Electricity consumption for mechanical processing | 36.89 | Electricity consumption for mechanical processing |
Fuel | MJ | 13,867.10 | From coal | 4271.84 | From preferred fuels (e.g. natural gas, LPG, etc.) |
Output | |||||
Products | kg | 825.25 | 942.60 | ||
Total solid waste | kg | 251.46 | 119.26 | ||
Coal slag | kg | 99.03 | – | ||
Metal slags | kg | 74.27 | – | ||
Metal waste (during mechanical process) (collected for recycling) | kg | 24.76 | 28.28 | ||
Impurities in scraps (paper, plastic, stone, rubber) | kg | 50.00 | Estimated 5 wt% of aluminum scraps [19] | – | |
Furnace lining (refractory waste) | kg | 3.40 | 3.88 | ||
Skimming or dross when cleaning of furnace | kg | – | 77.67 | ||
Filter dust | kg | – | 9.43 | ||
Total wastewater | kg | 14,461.13 | 2659.22 | ||
Wastewater (from cooling) | kg | 12,378.69 | 282.78 | ||
Wastewater (from surface treatment) | kg | 2082.44 | 2376.44 |
Selected BAT
Copper recycling
Current technology
Unit | Current technology | Selected BAT | |||
---|---|---|---|---|---|
Quantity | Note | Quantity | Note | ||
Input | |||||
Copper scraps | kg | 1000.00 | 1000.00 | ||
Sn | kg | 52.50 | Calculated based on the assumption of 1 wt% metals lost during melting and 0.1 wt% metals lost in air emission. | 54.35 | Calculated based on the assumption of 1 wt% metals lost during melting and 0.1 wt% metals lost in air emission |
Pb | kg | 31.50 | 32.61 | ||
Energy for mold heating, smelting and holding | MJ | 46,032.72 | 37,139.14 | ||
Energy for smelting and holding | MJ | 9223.84 | 1704.95 | Manual casting | |
Clay (recycled) | kg | 5095.76 | 5274.68 | ||
Clay (new) | kg | 566.20 | 586.08 | ||
Water | kg | 3088.34 | 3196.77 | ||
Output | |||||
Final Products | kg | 1029.45 | Half-length statues (as a bronze type) with Copper, Sn and Pb at the proportion of 92, 5 and 3%, respectively | 1065.59 | Half-length statues (as a bronze type) with Copper, Sn and Pb at the proportion of 92, 5 and 3%, respectively |
Pb, Sn in air emission | kg | 0.08 | 0.09 | ||
Equivalent CO2 emission | kg | 2959.31 | Calculated from data provided in Table 3. The CO2 emission from wood burning is not counted as a biomass source | 2030.53 | Calculated from data provided in Table 3. The CO2 emission from wood burning is not counted as a biomass source |
Total solid waste | kg | 882.08 | 740.79 | ||
Coal slag and ashes | kg | 205.89 | 125.89 | ||
Dust from filter to recycling | kg | – | 10.71 | With air treatment facility (filter bags) | |
Metal slags | kg | 100.00 | 15.98 | ||
Refractory lining waste | kg | – | 2.13 | ||
Solid waste (impurities such as paper, plastic, rock) | kg | 10.00 | – | ||
Solid waste (clay as mold materials) | kg | 566.20 | 586.08 | ||
Clay (to be recycled) | kg | 5095.76 | 5274.68 | ||
Copper loss in mechanical processes (cutting, polishing) to recycling | kg | 5.15 | Approximately 0.5 wt% output metal [19] | 5.33 | Approximately 0.5 wt% output metal [19] |
Selected BAT
Results for desktop PC recycling
Summarization of critical flows
Critical flow | Air emission | Wastewater | Solid waste | Improvement potential |
---|---|---|---|---|
PCB treatment | ||||
Gold recovery |
Toxic gases from acid leaching reactions such as NO
2
, Cl
2
. |
Wastewater (approximately 0.08 m
3
for 4.1 kg of high gold-contained parts from 1 t of treated PCBs) with residue acids, other chemicals, heavy metals. Especially, high copper content in wastewater
| Solid residues consisting of glass fiber and organics (3 kg per 4.1 kg of high gold-contained parts from 1 t of treated PCBs) | Protective equipment (mask) for workers Ventilation and air treatment system for acid leaching spots Solution with high copper content can be collected for further copper extraction. Wastewater collection and treatment system. For example, using Calcium hydroxide solution for residue acid neutralization and metal ion precipitation |
Copper recovery | Exhausted gas from gas combustion containing NO
x
, SO2 which is sucked by an electric fan and released into environment though a chimney | Wastewater (about 5 m3/t of treated PCBs) from water used for fine shredding and separating which is passed through sedimentation tank before discharged |
Non-copper residues containing glass fiber and organics (392.7 kg/t of treated PCBs)
| Wastewater collection and treatment for recycling purpose |
Ferrous metal recycling |
Dust consisting of metal dust and ferrous rust from cutting step
High air emission (dust, rust) from charging scraps into furnace
Gaseous emission containing metal and metal oxides, organic compounds and other gases such as CO, NO
x
during melting process
Dust released during removal of steel billets out from molds
| Wastewater from cooling water (5–7 m3/t of steel billets) | Impurities from scraps (12.5–14 kg/t of steel billet) Slag (20–25 or up to 45 kg/t of steel billets) Refractory waste | New smelter with better energy efficiency Potential to improve operation efficiency and minimize emission (scrap management options: scrap sorting; “first in, first out” principle, etc.; melting process control options: scrap size, material charging process, etc.) Water cooling tower for water recycling Air emission collection (e.g. suction hood above smelter) and treatment system |
Plastic recycling |
Dust formed during charging of shredded plastics into cone-shape funnel
Air pollutants (e.g. monomers, or other organic compounds) generated during extruding
| Wastewater from cooling water (21.7–51 m3/t of secondary plastic pellets) | Impurities (8–11 kg/t of secondary plastic pellets) Plastic pellets are scattered on the floor (37–40 kg/t of secondary plastic pellets) | Extruders with higher energy efficiency Better process control to improve energy efficiency (e.g. running at its most efficient speed, controlling electric motor to match the torque) Water cooling tower for water recycling Better ventilation system |
Aluminum recycling |
Dust generated from all “dry” steps: classifying, cutting, charging, melting, mold dissembling, sheet making, and residue cutting
Air emission consisting of metals and metal oxides, organic contaminants from incomplete combustion of organic matters during melting step
Other gaseous pollutants (e.g. CO, SO
2
, NO
x
) from coal combustion
|
Wastewater from cooling water (13–21 m
3
/t of final products, such as cookware, basins)
Wastewater from surface treatment contains toxic chemicals (e.g. metal, chromic acid, sulfuric acid or sodium hydroxide)
Wastewater bearing metals and other compounds from aluminum slag washing/separating to recovery metals in aluminum slag
|
Impurities (5 wt% of scraps)
Coal slags (15–20 wt% of consumed coal)
Metal slags (approximately 5–8 wt% of scraps
Refractory waste
| New technology smelter suitable for old scrap types (e.g. reverberatory furnaces) Scrap sorting Better coal quality to reduce generated waste Process control to improve energy efficiency (e.g. scrap cutting, better insulation, material charging process) Better process control to improve surface treatment steps: water and chemical saving (e.g. applied reverse-order washing principle in which water is supplied only at the cleanest tank (the last one) and run over the previous tank, dripping time increase for products after taking them out from surface treatment tanks) Water cooling tower for water recycling Air emission collection and treatment system Solid waste management program |
Copper recycling |
Dust containing metals, soils during scrap charging into smelters
Fume metals and metal oxides, organic compounds, CO, NO
2
, SO
2
during melting process
Generated dust, CO, other compounds from burning of materials from mold cover layer
Dust from mold dismantling and from mechanical process
Dust, volatile ash, CO, NO
2
, SO
2
, etc. from wood/coal combustion during mold heating process
|
Metals and other compounds polluted water bodies (ponds, water channels) from metal slag cleaning/separating activity to recovery metals in metal slag
|
Impurities from sorting of scraps (about 1 wt% of scraps)
Coal slags (15–20 wt% of consumed coal)
Metal slags (dross) (10–15 wt% of scraps or 2–5 wt% of final products)
Metal particles from mechanical processes (0.5 wt% of final products)
Mold materials (clay)
Refractory waste
| New technology smelter (e.g. Induction furnaces) Scrap sorting Process control to improve energy efficiency (e.g. scrap cutting, better insulation, material charging process) Air emission collection (e.g. suction hood above smelter) and treatment system Solid waste management program Water cooling tower for water recycling |
Comparison between two scenarios
Unit | Current technologies | Selected BAT | |
---|---|---|---|
Quantity | Quantity | ||
Energy consumption | |||
Electricity consumption | kWh | 747.731 | 439.387 |
Fuels (coal, LPG, wood) | MJ | 672.554 | 361.110 |
Waste stream | |||
Wastewater (total) | kg | 5743.700 | 47.754 |
Solid waste (total) | kg | 127.581 | 66.409 |
Equivalent CO2 emissions | kg | 401.689 | 239.988 |