How does sodium hydrosulfide (NaHS) differential flotation separate molybdenite (MoS2) from chalcopyrite (CuFeS2)?

In porphyry copper-molybdenum concentrators, both chalcopyrite (CuFeS2) and molybdenite (MoS2) float together into a bulk Cu-Mo sulfide concentrate. To separate them, sodium hydrosulfide (NaHS) or Nokes reagent is dosed into nitrogen-blanketed flotation cells to lower the pulp redox potential below -450 mV (SHE). This strips xanthate collector coatings off the chalcopyrite surfaces—causing copper and iron sulfides to sink as copper concentrate—while laminar MoS2 flakes remain naturally hydrophobic along their basal sulfur planes and float with non-polar hydrocarbon oils into a 50% to 54% Mo concentrate.

Why is pure molybdenum metal reduced in two hydrogen stages (550°C then 1,050°C), and how is 5N MoS2 used in sub-2 nm transistors?

Technical MoO3 is leached in aqueous ammonia to reject insoluble Fe/Si/Cu gangue and crystallized into pure ammonium dimolybdate (ADM, (NH4)2Mo2O7). Stage-one hydrogen reduction at 550°C converts ADM/MoO3 into non-volatile MoO2 before stage-two reduction at 1,050°C produces 99.95% Mo metal powder, preventing MoO3 sublimation. Sublimed 5N MoO3 and MoCl5 precursors are also used in MOCVD reactors to grow 0.65 nm monolayer 2D MoS2 channels with a 1.8 eV direct bandgap for sub-2 nm gate-all-around (GAA) nanosheet logic.

Molybdenum Refining, Ferromolybdenum & 2D MoS2 Lab

Q: Why must multiple-hearth Herreshoff roasting of MoS2 be strictly controlled between 600°C and 650°C?

Oxidative roasting of molybdenite (2MoS2 + 7O2 -> 2MoO3 + 4SO2) is strongly exothermic (Delta H = -2,218 kJ/mol). If hearth temperatures exceed 680°C to 700°C, molybdenum trioxide (MoO3) develops high vapor pressure and sublimes rapidly, while localized hot spots approaching its 795°C melting point fuse the calcine bed onto the rabble arms and react with residual copper and calcium to form ammonia-insoluble CuMoO4 and CaMoO4 phases.

Q: How are rhenium (Re) and sulfuric acid recovered from molybdenite roaster off-gas?

Rhenium disulfide (ReS2) is lattice-substituted inside porphyry molybdenite at 200 to 1,000 ppm Re. During 630°C oxidative roasting, ReS2 oxidizes into volatile rhenium heptoxide (Re2O7, boiling point 360°C), which exits in the SO2-rich roaster exhaust gas. Wet venturi scrubbers ahead of the sulfuric acid plant capture Re2O7 as aqueous perrhenic acid (HReO4), which is recovered on strong-base anion-exchange resins and crystallized as ammonium perrhenate (NH4ReO4), while cleaned SO2 gas is catalytically oxidized to 98% H2SO4.

Q: How is ferromolybdenum (FeMo, 60–70% Mo) smelted via silicothermic-aluminothermic reduction?

Technical molybdic oxide (Tech MoO3) is blended with ferrosilicon (FeSi75), aluminum granules, iron ore/mill scale (Fe2O3), and fluorspar/lime flux inside a refractory-lined reaction pot. Once ignited, the exothermic metallothermic reduction (3MoO3 + 2Al + 9/4 Si + Fe2O3 -> FeMo + Al2O3-SiO2 slag) reaches >1,950°C without external electric arc heating, settling dense molten ferromolybdenum (65% Mo) beneath a fluid aluminosilicate slag.

Total Saleable Mo

18,019 t/yr

Tech MoO3: 30,529 t/yr | Overall Rec: 88.3%

FeMo Alloy (65% Mo)

16,669 t/yr

10,835 t Mo | Enables 492 kt HSLA/316L Steel

99.95% Mo & 5N MoS₂

7,184 t/yr

ADM: 12,715 t | 38,913 t HDS Catalyst

Annual Revenue

$1,231.02M

EBITDA: $1,054.51M (85.7% Margin)

20-Yr Project NPV

$7,274.88M

IRR: 132.8% | Payback: 0.8 yrs

Net Mo AISC

$8.92/kg

Net of 9,876 kg Re & 36.3 kt H2SO4

Roaster & Refinery Controls

Bulk Sulfide / Concentrator Feed 240 kt/yr

Bulk Cu-Mo sulfide or primary porphyry MoS₂ feed tonnage

Feed Contained Molybdenum Grade 8.5% Mo

Contained Mo in bulk Cu-Mo concentrate / high-grade feed

NaHS Differential Flotation Recovery 91.5%

Cu depression at Eh < -450 mV to 52% Mo (86.7% MoS₂) conc

630°C Herreshoff Roaster Recovery 98.2%

Multiple-hearth MoS₂ oxidation to Tech MoO₃ with ESP dust recycle

FeMo vs ADM / 99.95% Mo Split 60% FeMo / 40% ADM-Mo

Share of Tech MoO₃ routed to silicothermic FeMo vs NH₃ leach & H₂ reduction

FeMo Price ($/kg Contained Mo) $48/kg

Realized price per kg contained Mo in 65% FeMo alloy

99.95% Mo / 5N MoS₂ Price ($/kg Mo) $95/kg

Blended price across ADM catalyst, TZM metal, and 5N 2D MoS₂ precursors

Integrated Plant CAPEX ($M) $580M

NaHS flotation, Herreshoff roaster, Re scrubber, H₂SO₄ plant, FeMo & H₂ furnaces

Discount Rate / WACC (%) 8.5%

Real weighted average cost of capital for 20-year DCF

Interactive MoS₂ Roasting, Re₂O₇ Scrubbing, FeMo & 2D MoS₂ Flowsheet

2MoS₂ + 7O₂ → 2MoO₃ + 4SO₂↑

Stage-by-stage molybdenum mass balance, rhenium and sulfuric acid byproduct recovery, and operating cash flow breakdown
Unit Operation / Process Stage	Feed / Reaction Basis	Mass Output / Yield	Financial Contribution

20-Year discounted cash flow schedule for integrated molybdenum roasting, FeMo smelting, and ADM hydrogen reduction
Year	Saleable Mo (t)	FeMo Alloy (t)	99.95% Mo (t)	Rhenium (kg)	Revenue	OPEX	EBITDA	Taxes	Free Cash Flow	Cum. FCF

20-Year Project Net Present Value (NPV) across Sulfide Feed Molybdenum Grade ($\pm 2.0\%\ \text{Mo}$) vs. Realized $\text{FeMo}$ & $99.95\%\ \text{Mo}$ Market Prices ($\pm 20\%$). Base case cell is outlined in bold.

5 by 5 sensitivity matrix of 20-year project NPV across feed Mo grade and molybdenum market prices
Feed Grade \ Mo Price	-20% Price	-10% Price	Base Price	+10% Price	+20% Price

Extractive Metallurgy, Roaster Thermodynamics & 2D MoS₂ Mastery Quiz

Score: 0 / 4

First-Principles Process Engineering, Metallurgy & Semiconductor Physics

1. Multiple-Hearth Herreshoff Oxidative Roasting & Re₂O₇ Capture

Flotation molybdenite concentrate ($50\text{–}54\%\ \text{Mo}$, $85\text{–}90\%\ \text{MoS}_2$) is fed to the top hearth of a 10- to 12-hearth vertical Herreshoff furnace and rabbled downward counter-current to air at $600\text{–}650^\circ\text{C}$:

2 {MoS}_{2} + 7 O_{2} \overset{630 ° C}{\to} 2 {MoO}_{3} + 4 {SO}_{2} ↑ (Δ H^{\circ} = - 2,218 kJ/mol)

Strict hearth cooling prevents $\text{MoO}_3$ sublimation ($>700^\circ\text{C}$) and bed fusion ($795^\circ\text{C}$). Isomorphic rhenium disulfide ($\text{ReS}_2$) oxidizes into volatile $\text{Re}_2\text{O}_7$ (b.p. $360^\circ\text{C}$), which is scrubbed from the $\text{SO}_2$ gas stream as perrhenic acid ($\text{HReO}_4$) and crystallized via anion exchange as ammonium perrhenate ($\text{NH}_4\text{ReO}_4$).

2. Silicothermic FeMo Smelting, Two-Stage H₂ Reduction & 2D MoS₂

Technical $\text{MoO}_3$ is either smelted exothermically with ferrosilicon ($\text{FeSi}_{75}$) and aluminum into $65\%\ \text{Mo}$ ferromolybdenum ($\text{FeMo}$) for pitting-resistant steels, or leached in aqueous $\text{NH}_3$ to crystallize ammonium dimolybdate ($\text{ADM}$) for two-stage hydrogen reduction:

{MoO}_{3} + H_{2} \overset{550 ° C}{\to} {MoO}_{2} + H_{2} O \Rightarrow {MoO}_{2} + 2 H_{2} \overset{1,050 ° C}{\to} Mo (99.95%) + 2 H_{2} O

In stainless and sour-gas pipeline steels, molybdenum carries a $3.3\times$ multiplier in the Pitting Resistance Equivalent Number ($\text{PREN} = \%\text{Cr} + 3.3[\%\text{Mo}] + 16[\%\text{N}]$). In advanced logic, $5\text{N}$ $\text{MoO}_3/\text{MoCl}_5$ precursors grow $0.65\text{ nm}$ monolayer 2D $\text{MoS}_2$ channels ($E_g \approx 1.8\text{ eV}$) that eliminate short-channel leakage in sub-$2\text{ nm}$ gate-all-around (GAA) transistors.

Frequently Asked Questions: Molybdenum Refining, FeMo & 2D MoS₂

In porphyry copper-molybdenum concentrators, both chalcopyrite ($\text{CuFeS}_2$) and molybdenite ($\text{MoS}_2$) float together into a bulk $\text{Cu-Mo}$ sulfide concentrate. To separate them, sodium hydrosulfide ($\text{NaHS}$) or Nokes reagent is dosed into nitrogen-blanketed flotation cells to lower the pulp redox potential below $-450\text{ mV}$ ($\text{SHE}$). This strips xanthate collector coatings off the chalcopyrite surfaces—causing copper and iron sulfides to sink as copper concentrate—while laminar $\text{MoS}_2$ flakes remain naturally hydrophobic along their basal sulfur planes and float with non-polar hydrocarbon oils into a $50\%$ to $54\%\ \text{Mo}$ concentrate.

Oxidative roasting of molybdenite ($2\text{MoS}_2 + 7\text{O}_2 \rightarrow 2\text{MoO}_3 + 4\text{SO}_2$) is strongly exothermic ($\Delta H^\circ = -2,218\text{ kJ/mol}$). If hearth temperatures exceed $680^\circ\text{C}$ to $700^\circ\text{C}$, molybdenum trioxide ($\text{MoO}_3$) develops high vapor pressure and sublimes rapidly, while localized hot spots approaching its $795^\circ\text{C}$ melting point fuse the calcine bed onto the rabble arms and react with residual copper and calcium to form ammonia-insoluble $\text{CuMoO}_4$ and $\text{CaMoO}_4$ phases.

Rhenium disulfide ($\text{ReS}_2$) is lattice-substituted inside porphyry molybdenite at $200$ to $1,000\text{ ppm Re}$. During $630^\circ\text{C}$ oxidative roasting, $\text{ReS}_2$ oxidizes into volatile rhenium heptoxide ($\text{Re}_2\text{O}_7$, boiling point $360^\circ\text{C}$), which exits in the $\text{SO}_2$-rich roaster exhaust gas. Wet venturi scrubbers ahead of the sulfuric acid plant capture $\text{Re}_2\text{O}_7$ as aqueous perrhenic acid ($\text{HReO}_4$), which is recovered on strong-base anion-exchange resins and crystallized as ammonium perrhenate ($\text{NH}_4\text{ReO}_4$), while cleaned $\text{SO}_2$ gas is catalytically oxidized to $98\%\ \text{H}_2\text{SO}_4$.

Technical molybdic oxide ($\text{Tech MoO}_3$) is blended with ferrosilicon ($\text{FeSi}_{75}$), aluminum granules, iron ore/mill scale ($\text{Fe}_2\text{O}_3$), and fluorspar/lime flux inside a refractory-lined reaction pot. Once ignited, the exothermic metallothermic reduction ($3\text{MoO}_3 + 2\text{Al} + \frac{9}{4}\text{Si} + \text{Fe}_2\text{O}_3 \rightarrow \text{FeMo} + \text{Al}_2\text{O}_3\text{-SiO}_2\text{ slag}$) reaches $>1,950^\circ\text{C}$ without external electric arc heating, settling dense molten ferromolybdenum ($65\%\ \text{Mo}$) beneath a fluid aluminosilicate slag.

Technical $\text{MoO}_3$ is leached in aqueous ammonia to reject insoluble $\text{Fe/Si/Cu}$ gangue and crystallized into pure ammonium dimolybdate ($\text{ADM}$, $(\text{NH}_4)_2\text{Mo}_2\text{O}_7$). Stage-one hydrogen reduction at $550^\circ\text{C}$ converts $\text{ADM}/\text{MoO}_3$ into non-volatile $\text{MoO}_2$ before stage-two reduction at $1,050^\circ\text{C}$ produces $99.95\%\ \text{Mo}$ metal powder, preventing $\text{MoO}_3$ sublimation. Sublimed $5\text{N}$ $\text{MoO}_3$ and $\text{MoCl}_5$ precursors are also used in MOCVD reactors to grow $0.65\text{ nm}$ monolayer 2D $\text{MoS}_2$ channels with a $1.8\text{ eV}$ direct bandgap for sub-$2\text{ nm}$ gate-all-around (GAA) nanosheet logic.