Industrial Refinery & 6N/7N Semiconductor Presets
Load calibrated zinc RLE cementation cake and high-purity vacuum distillation benchmarks:
Total Refined Cadmium
1,318.4 t/yr Cd
629.5 t 4N + 688.8 t 6N/7N
6N/7N Semiconductor Cd
688.8 t/yr 6N/7N
Enables ~19.5 GW/yr CdTe Solar PV
Returned Zn & 4N Tl
3,672 t/yr Zn
+ 12.5 t/yr 4N Thallium (Tl)
Annual EBITDA
$35.49M
52.7% EBITDA Margin | Rev: $67.35M
20-Year Project NPV
$172.84M
IRR: 26.8% | Payback: 3.8 yrs
Net LCOCd (After Zn/Tl)
$16.12/kg
1.40 MWh/t Cd EW | 9,708 MWh/yr
1. Cu-Cd Cementation Cake, Electrowinning & 6N Distillation
8,500 t/yr
16.5% Cd
45.0% Zn
0.18% Tl
94.0%
2.60 V
88.5%
95.0%
2. Semiconductor Pricing, By-Product Credits & CAPEX
$4.80/kg
$78/kg
$1,450/t
$420/kg
$1,450/t
$65/MWh
$105M
8.5%
Interactive Cu-Cd Leach, Electrowinning & 6N/7N Vacuum Distillation Flowsheet
Tb(Cd) = 767°C | CdTe Eg = 1.45 eV| Process Parameter | Output / Metric |
|---|---|
| Cu-Cd Cementation Cake Feed | 8,500 t/yr |
| Contained Metals in Cake | 1,402.5 t Cd / 3,825 t Zn / 15.3 t Tl |
| Secondary Zn Dust Required | 858.8 t/yr Zn dust (1.12× stoich) |
| 4N Electrowon Cathode Cd | 1,318.4 t/yr 4N Cd (94.0% rec) |
| Specific Cd EW Energy | 1.40 MWh/t Cd (1,847 MWh/yr) |
| Commercial 4N Cd Sticks/Balls | 629.5 t/yr (629,512 kg/yr) |
| 6N/7N Semiconductor Cd Shot | 688.8 t/yr (688,838 kg/yr) |
| CdTe PV & CZT Allocation | 1,250.1 t/yr CdTe (~19.5 GW PV) + 103.3 t CZT Cd |
| Returned ZnSO4 & 4N Tl | 3,672 t/yr Zn + 12.5 t/yr 4N Tl |
| Revenue / Cost Line | Annual ($M/yr) |
|---|---|
| 6N/7N Semiconductor Cd & CdTe | $53.73M |
| 4N Commercial Cadmium | $3.02M |
| Returned ZnSO4 Tankhouse Credit | $5.32M |
| Co-Product 4N Thallium (Tl) Credit | $5.27M |
| Total Gross Revenue | $67.35M |
| Cu-Cd Cake Feedstock Transfer Cost | $12.33M |
| H2SO4 Leach, KMnO4 & EW Reagents | $3.71M |
| 6N/7N Quartz Distillation & Zone Gas | $7.92M |
| Refinery Electricity Cost | $0.63M |
| Fixed O&M, Closed-Loop EHS & Labor | $8.13M |
| Total Operating Cost (OPEX) | $32.71M |
| Annual EBITDA (Margin) | $34.64M (51.4%) |
20-Year Project NPV & IRR Sensitivity Matrix: Cake Cd Grade vs. 6N/7N Cd & CdTe Price
20-Year Discounted Cash Flow (DCF) Pro-Forma Schedule
10-Year Straight-Line Depreciation | 21% Corporate Tax | 1.5%/yr Escalation| Year | Total Cd (t) | 6N/7N Cd (t) | Revenue ($M) | OPEX ($M) | EBITDA ($M) | Taxes ($M) | Free Cash Flow ($M) | Discounted FCF ($M) | Cumulative FCF ($M) |
|---|
Governing Hydrometallurgical, Electrowinning & Vacuum Distillation Equations
1. Zinc-Dust Galvanic Cementation
Metallic zinc dust (E° = −0.763 V) spontaneously reduces dissolved cadmium ions (E° = −0.403 V) in neutral sulfate solution:
Stoichiometric zinc consumption is MZn / MCd = 65.38 / 112.41 = 0.582 t Zn per tonne Cd (ΔE° = +0.360 V).
2. Cadmium Sulfate Electrowinning
Purified CdSO4 electrolyte is electrowon onto aluminum cathodes using Pb-Ag anodes (n = 2 e−, 476.84 kAh/t Cd):
At Vcell = 2.60 V and ηI = 88.5%, specific electrolysis energy is 1.40 MWh/t 4N Cd.
3. 6N/7N CdTe Semiconductor Synthesis
Vacuum-distilled 6N/7N cadmium (Tb = 767°C) reacts directly with 6N tellurium to form stoichiometric cadmium telluride:
CdTe is 46.84 wt% Cd and 53.16 wt% Te, with a direct optical bandgap Eg = 1.45 eV and melting point of 1,092°C.
Cadmium Hydrometallurgy, Vacuum Distillation & CdTe / CZT Mastery Quiz
Frequently Asked Questions (FAQ)
Cadmium forms no economically minable primary ore deposits of its own; instead, Cd2+ isomorphously substitutes for Zn2+ in sphalerite (ZnS) concentrates at 0.1% to 0.5% Cd. During zinc roast-leach-electrowin (RLE) processing, dissolved cadmium must be quantitatively stripped from the neutral ZnSO4 electrolyte via metallic zinc-dust cementation (Cd2+ + Zn0 → Cd0 + Zn2+) so that cadmium does not co-deposit and embrittle the zinc cathode.
The cold-stage Cu-Cd-Zn filter cake (10–25% Cd, 40–60% Zn, 2–8% Cu, trace Tl) is oxidatively leached in dilute H2SO4 using air or oxygen, leaving copper behind in the leach residue. Trace lead and thallium are precipitated using KMnO4 and BaCO3/SrCO3, and a secondary stoichiometric zinc-dust cementation precipitates high-grade cadmium sponge (>90% Cd). The sponge is redissolved in spent cadmium electrolyte and electrowon onto aluminum cathodes using Pb-Ag anodes at 2.5–2.7 V (~1.4 MWh/t Cd), while the zinc-rich filtrate returns to the main zinc tankhouse.
Because cadmium has a low melting point (321.1°C) and a remarkably low boiling point (767°C at 1 atm) compared to heavy metal impurities (Pb, Cu, Tl, Bi, Ag, Sn), 4N cathode cadmium is distilled under high vacuum (10−2 to 10−4 mbar at 420–480°C) in multi-stage quartz or high-purity graphite retorts. Volatile trace zinc is rejected in a light fore-cut, heavy metals remain in the non-volatile distillation heel, and the distilled cadmium undergoes horizontal multi-pass zone refining under ultra-pure H2/Ar to reach 6N–7N purity.
Because zinc refineries must extract cadmium from sphalerite regardless of downstream market demand, converting by-product cadmium into cadmium telluride (CdTe) sequesters soluble heavy metal into an extremely stable, water-insoluble, non-volatile covalent semiconductor compound (melting point 1,092°C, Ksp ≈ 10−34) hermetically sealed between two glass sheets. At ~30 tonnes Cd per GW, a single 1,300 t/yr refinery supplies nearly 20 GW/yr of low-carbon utility solar PV with >90% end-of-life closed-loop chemical recycling.
Alloying 7N cadmium, zinc, and tellurium via Traveling Heater Method (THM) or High-Pressure Bridgman growth yields wide-bandgap (Eg ≈ 1.57 eV), high-atomic-number (ZCd = 48, ZTe = 52) single-crystal Cd1−xZnxTe (CZT). Unlike conventional indirect scintillator detectors, CZT directly converts individual X-ray and gamma photons into electrical charge pulses at room temperature with ultra-high energy resolution, enabling photon-counting computed tomography (PCCT) medical scanners that cut patient radiation dose by 30–50%.