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Nickel & Cobalt Concentrate Assay
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Sterling Analytical provides nickel and cobalt concentrate assay, quantifying payable metal grade alongside the penalty elements that determine smelter acceptance terms and contract economics. Our ICP-OES testing serves mining operators, concentrate traders, and smelters who need both halves of the commercial picture a concentrate represents — not just how much nickel and cobalt are present, but which deleterious elements are present alongside them, since both numbers together determine what a given lot is actually worth.
Nickel sulfide concentrate is produced by flotation from sulfide ore, concentrating nickel along with cobalt (which generally substitutes into the same pentlandite mineral structure as nickel) and frequently platinum group metals as well. The resulting concentrate is sold to smelters under contract terms that pay for recoverable metal content but penalize specific impurity elements — sometimes severely, and in some cases to the point of outright rejecting a lot regardless of the metal value it carries. Understanding and managing this payable-metal-versus-penalty-element balance is central to how nickel and cobalt concentrate is actually bought, sold, and valued in practice.
How Smelter Contracts Actually Price a Concentrate: Payable Metals and Penalty Elements
This is worth explaining in some detail, because it’s the commercial logic underneath everything else on this page, and it’s not obvious if you’re new to concentrate trading.
A smelter purchase contract pays the seller for “payable” metal content — typically nickel and cobalt, sometimes with platinum group metal credits — but applies penalties for elements that cause problems in the smelting process itself. Common penalty elements include arsenic, mercury, and magnesium (as magnesia, MgO), among others, with penalty severity generally escalating as concentration rises. Some smelters will reject a lot outright if a single impurity is high enough, regardless of how attractive the overall metal grade looks.
There’s a specific, easy-to-miss economic detail here worth understanding directly: when an element is penalized, the metal value within that penalized element generally isn’t paid for either — what the industry sometimes describes as a “double” cost to the concentrate producer. A penalty on excessive nickel content itself (which can occur in certain contexts) might look modest as a stated penalty rate, but the lost nickel payment underneath it can be the more financially significant part of the loss. This is part of why an accurate, comprehensive assay matters as much for what it rules out as for what it confirms — knowing your penalty element profile in advance, before a lot reaches a smelter’s own incoming assay, gives you the chance to negotiate, blend, or reprocess rather than absorb an unexpected penalty after the fact.
Matrix & Digestion
Nickel and cobalt sulfide concentrate requires complete digestion across both the sulfide mineral phase carrying the value metals and any silicate gangue carried over from incomplete flotation separation.
Sterling Analytical’s approach:
- Multi-acid digestion for complete dissolution of sulfide minerals (commonly pentlandite, with associated pyrrhotite and chalcopyrite)
- Hydrofluoric acid (HF) where silicate gangue content requires it, particularly relevant for concentrates carrying magnesium-bearing silicate minerals like serpentine or talc
- Oxidative treatment appropriate to sulfide matrix breakdown
- Method validation suited to the specific mineralogy of your concentrate, since nickel sulfide ore bodies vary meaningfully in associated gangue mineralogy from one deposit to another
What We Test For
- Payable metals : Nickel (Ni), Cobalt (Co), and platinum group metals where present (Pt, Pd)
- Common penalty elements : Arsenic (As), Mercury (Hg), Magnesium (as MgO), Lead (Pb), Cadmium (Cd), Fluorine (F), Silica (SiO2)
- Smelter process-relevant elements : Sulfur (S), Iron (Fe), Copper (Cu)
- Additional trace elements : Available on request depending on buyer specification
Magnesia (MgO) deserves particular attention as a penalty consideration distinct from most other penalty elements: it isn’t toxic or environmentally hazardous the way arsenic or mercury are, but elevated magnesia raises slag viscosity during smelting and causes real operational problems — poor slag-matte separation and increased metal losses to slag — making it a penalty element for process reasons rather than safety or regulatory ones.
Why Cobalt Recovery Deserves Its Own Attention
Cobalt in nickel sulfide concentrate behaves differently from nickel during smelting in a way that’s worth understanding when interpreting an assay result, not just generating one. Cobalt typically substitutes into the pentlandite mineral structure alongside nickel and reports to the same concentrate, but it doesn’t recover to the smelter matte phase nearly as efficiently as nickel does — published industry figures suggest 30 to 50 percent of cobalt can be lost to metallurgical slag during conventional smelting and converting, a substantially worse recovery rate than nickel typically experiences through the same process.
This matters commercially because a concentrate’s assayed cobalt grade and its actual payable cobalt value aren’t the same thing — payment terms generally account for expected smelter recovery rates, not just contained metal. Understanding this distinction is part of why an accurate, independently verified cobalt assay matters even though the smelter, not the assay, ultimately determines how much of that cobalt is actually recovered.
Platinum Group Metal Association: An Often-Overlooked Value Stream
Nickel sulfide concentrates frequently carry platinum group metals as a genuine, sometimes underappreciated value component, and understanding how these elements distribute mineralogically helps frame what an assay can tell you.
Palladium tends to associate closely with pentlandite — the same nickel-iron sulfide mineral hosting most of the nickel and cobalt — and generally reports to the nickel concentrate along with them. Platinum behaves somewhat differently: it’s often present as discrete platinum-group minerals, or in some deposits occurs within pyrrhotite, a sulfide mineral that’s typically less economically significant and can make platinum harder to recover efficiently depending on the specific mineralogy involved. Gold, where present, is usually found as free gold and can report to either nickel or copper concentrate streams depending on flotation circuit behavior.
This means two nickel concentrates with similar nickel and cobalt grades can carry meaningfully different platinum group metal value depending on deposit-specific mineralogy, and a complete assay — rather than one limited to nickel and cobalt alone — is often the only way to identify that value before it’s left on the table in a transaction that doesn’t account for it.
Common Quality and Commercial Issues We Identify
- Penalty elements (As, Hg, Mg) at levels that would trigger meaningful contract penalties or smelter rejection
- Magnesia content elevated due to gangue mineral entrainment (serpentine, talc) from incomplete flotation selectivity
- Nickel and cobalt grade inconsistent with expected ore body characteristics, useful for process or blending decisions
- Sulfur content relevant to smelter processing requirements and SO2 management
- Lot-to-lot variability suggesting blending opportunities or process adjustments worth investigating before shipment
Who Uses This Service
- Mining operators verifying concentrate quality before shipment to smelters, using assay data to anticipate penalty exposure and negotiate contract terms from an informed position rather than discovering issues at the smelter gate.
- Concentrate traders requiring independent, defensible assay data to support purchase and resale transactions, where payable metal and penalty element accuracy directly determines transaction value.
- Smelters and processors conducting incoming quality verification or arbitration assay when results from a supplier's certificate are in question.
- Junior mining and exploration companiescharacterizing pilot-scale concentrate samples during metallurgical test work, supporting flowsheet development and early off-take discussions with potential smelter partners.
- Process engineersinvestigating flotation circuit performance, using gangue-related penalty element trends (particularly magnesia) to evaluate selectivity and guide circuit optimization.
Sample Quantity & Handling
Required sample size: 50–100 grams of representative concentrate.
Packaging guidelines:
- Use sealed, clean containers appropriate for sulfide mineral concentrate
- Ensure the sample is genuinely representative — concentrate composition can vary across a shipment or stockpile, so a composite sample is more reliable than a single grab sample, particularly given how directly grade and penalty element results affect commercial outcomes
- Clearly label source, deposit, and processing details where known
Turnaround Time & Pricing
Standard turnaround: 3–5 business days Rush service: 24–48 hours available
Pricing starts from $150 per sample, depending on element panel and whether platinum group metal analysis is included.
What You Receive
Clients receive a detailed Certificate of Analysis (COA) suitable for commercial transactions, smelter contract negotiation, and process evaluation.
Your COA includes:
- Payable metal grade (Ni, Co, and PGMs where applicable)
- Full penalty element panel (As, Hg, Mg, Pb, Cd, F, SiO2, and others as scoped)
- Method references and digestion notes
- Reporting limits and analytical qualifiers
- Batch-level quality control summary
All results are supported by CRM-traceable calibration, with duplicates and matrix spikes performed on each analytical batch — important when results are tied directly to commercial settlement or smelter contract terms.
Methods & Standards
Sterling Analytical applies established methods adapted for nickel and cobalt sulfide concentrates:
- Multi-acid digestion suited to sulfide mineral matrices
- ICP-OES elemental analysis (SW-846 6010 framework)
- Calibration using certified reference materials (CRMs)
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Frequently Asked Questions
It's used to determine payable metal grade (nickel, cobalt, and platinum group metals where present) alongside penalty element content (arsenic, mercury, magnesia, and others), supporting smelter contract negotiation, commercial transactions, and process evaluation.
Penalty elements are impurities that cause problems during smelting and are penalized financially under smelter contracts, sometimes severely enough to trigger outright rejection of a lot. Common examples include arsenic, mercury, and magnesia. When an element is penalized, the metal value associated with it is typically not paid either, compounding the financial impact.
Elevated magnesia raises slag viscosity during smelting, causing poor slag-matte separation and increased metal losses to slag. It's penalized for process and operational reasons rather than safety or environmental ones.
Cobalt recovers to smelter matte less efficiently than nickel during conventional smelting and converting, with published estimates suggesting 30-50% can be lost to slag. Payment terms generally account for expected recovery rates, not just contained metal, which is why assayed grade and payable value aren't identical.
50–100 grams of representative concentrate, ideally composited from multiple points in a shipment or stockpile.
Standard turnaround is 3–5 business days, with 24–48 hour rush service available.
Yes. Palladium frequently associates with the same pentlandite mineral hosting nickel and cobalt, while platinum and gold distribution varies by deposit mineralogy. Two concentrates with similar nickel and cobalt grades can carry different PGM value, which a complete assay can help identify.
Yes. Nickel sulfide concentrates frequently carry associated platinum and palladium, which can be included in the analytical panel where relevant to your concentrate source.
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