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Mixed Hydroxide Precipitate (MHP) Testing
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Sterling Analytical provides mixed hydroxide precipitate (MHP) testing, quantifying nickel and cobalt grade alongside the iron, manganese, and magnesium content that determines MHP quality and downstream processing requirements. MHP has become one of the most important intermediate products in battery-grade nickel and cobalt supply, produced from nickel laterite ore through high-pressure acid leaching (HPAL) and increasingly treated as a near-equivalent to Class 1 nickel for battery cathode applications.
The HPAL route that produces MHP is a genuinely significant upgrading process: laterite ore typically containing around 1% nickel and 0.8% cobalt is leached, purified, and precipitated into MHP running roughly 40% nickel and 3% cobalt — a substantial concentration of value into a much smaller, more processable material. But that upgrading process doesn’t remove every impurity equally well, and the specific impurities that remain — iron, manganese, magnesium chief among them — directly affect how much further processing MHP needs before it’s suitable for battery-grade nickel and cobalt sulfate production.
Our laboratory supports nickel laterite processors, battery materials refiners, and traders handling MHP at various points in this supply chain, from initial HPAL plant output through to material ready for sale or further refining.
How MHP Is Made, and Why It Matters for What You're Testing
Understanding the HPAL process that produces MHP helps make sense of what a given MHP sample’s composition actually tells you. Laterite ore is leached with sulfuric acid at high temperature and pressure (commonly around 250°C), producing a pregnant leach solution (PLS) containing nickel, cobalt, and a substantial amount of dissolved iron — iron is typically the single largest impurity in the leach solution by mass, since laterite ores are iron-rich. Before nickel and cobalt can be precipitated as MHP, this iron has to be selectively removed, generally through pH-controlled precipitation that takes advantage of iron’s different precipitation behavior relative to nickel and cobalt.
Once iron removal is complete, the purified solution is neutralized — commonly with magnesium oxide, lime, or sodium hydroxide — to precipitate nickel and cobalt together as mixed hydroxides. This is where MHP gets its name, and where its remaining impurity profile is largely set. Manganese, when present in the leach solution, tends to co-precipitate with nickel and cobalt through what’s understood to be an oxidative mechanism distinct from straightforward hydroxide precipitation, which is part of why manganese content can be sensitive to precipitation conditions in ways that are harder to control than a simple pH adjustment might suggest.
What We Test For
- Nickel (Ni) : Primary value metal, typically ~35-45% in finished MHP
- Cobalt (Co) : Primary value metal, typically ~2-4% in finished MHP
- Iron (Fe) : Dominant impurity carried over from incomplete iron removal upstream
- Manganese (Mn): Co-precipitating impurity, sensitive to precipitation chemistry
- Magnesium (Mg) : Process-derived impurity, often from MgO used as precipitation reagent
- Calcium (Ca) : Process-derived impurity, particularly where lime is used for precipitation
- Zinc (Zn) : Minor impurity, relevant to refining requirements
- Copper (Cu) : Minor impurity
- Sulfate / Chloride : Anion content relevant to downstream processing route
Nickel and cobalt grade are reported as the primary value metrics, with the full impurity panel providing the data needed to assess refining requirements and material value.
Why Iron Content Is the First Thing We Look At
Iron deserves particular attention in MHP testing because it’s both the most abundant impurity and the one most directly tied to upstream process performance. Since laterite ore is iron-rich and iron has to be removed from the pregnant leach solution before nickel and cobalt precipitation, the iron level in a finished MHP sample is essentially a report card on how well that upstream iron removal step performed.
Elevated iron in MHP isn’t just a grade dilution issue — it adds real cost and complexity to downstream refining, since further iron removal is generally required before the material can be processed into battery-grade nickel and cobalt sulfate. A consistent pattern of elevated iron across multiple MHP lots from the same source can point toward a systematic upstream process issue worth investigating, rather than normal lot-to-lot variation.
MHP vs. MSP: Why the Distinction Matters for Interpreting Results
MHP isn’t the only intermediate product HPAL operations can choose to produce. Mixed sulfide precipitate (MSP) is the main alternative, made by treating the same pregnant leach solution with hydrogen sulfide instead of a basic precipitation reagent. MSP typically runs at higher nickel grade (around 55% nickel is a commonly cited figure) than MHP, but the hydrogen sulfide process used to produce it involves handling a genuinely hazardous gas, which has made some operators favor MHP despite its somewhat lower grade and higher impurity load.
This matters for interpreting MHP test results because the two materials aren’t directly comparable on a simple grade basis — MHP’s lower nickel percentage relative to MSP reflects the precipitation chemistry used to produce it, not necessarily a quality problem, and MHP has increasingly proven capable of being processed through the same downstream refining equipment used for nickel briquettes, powder, or oxide, which is part of why it gained industry acceptance despite carrying higher impurity levels than some alternatives. Understanding which intermediate product a given sample represents — and what grade and impurity profile is actually typical for that product — matters more than comparing raw numbers across different intermediate types.
Common Quality Issues We Identify
- Elevated iron content indicating incomplete upstream iron removal during HPAL processing
- Manganese levels inconsistent with expected precipitation chemistry, sometimes pointing to oxidation-reduction conditions during precipitation that warrant process review
- Magnesium or calcium content reflecting precipitation reagent carryover, relevant to refining route selection — material precipitated with MgO, for instance, will typically carry a different magnesium signature than material precipitated with lime
- Nickel and cobalt grade below expected specification, affecting material valuation
- Lot-to-lot inconsistency from a single source, suggesting process variability worth tracking over time rather than dismissing as one-off sampling noise
- Moisture content discrepancies between reported dry-basis grade and actual wet filter cake composition, relevant when material changes hands based on a dry-basis specification
Who Uses This Service
- HPAL plant operators monitoring MHP product quality as a direct indicator of upstream process performance, particularly iron removal effectiveness, using composition trends to catch process drift before it compounds across multiple production lots.
- Battery materials refiners screening incoming MHP feedstock before committing it to nickel and cobalt sulfate conversion, where impurity profile affects refining cost, reagent consumption, and overall process economics.
- Metal traders requiring independent, defensible composition data to support MHP transactions, where nickel and cobalt grade directly determine material value and where both buyer and seller benefit from testing performed against a consistent, neutral methodology.
- Battery supply chain procurement teams evaluating MHP as a Class 1 nickel alternative, comparing composition and impurity profile against sulfide-derived material or MSP to inform sourcing decisions and supplier qualification.
- Process engineers investigating precipitation chemistry issues, using manganese and other impurity trends to understand precipitation conditions, evaluate reagent choice (MgO versus lime versus NaOH), and optimize overall circuit performance.
Sample Quantity & Packaging
Required sample size: 10–20 grams of representative MHP, typically as a wet or dried filter cake.
Packaging guidelines:
- Use sealed HDPE or polypropylene containers
- For wet filter cake samples, minimize air exposure and consider noting moisture content at time of sampling, since this affects how results should be interpreted relative to a dry-basis specification
- Ensure the sample is representative — MHP can show real compositional variation across a single production lot, particularly for iron and manganese
- Clearly label source, production date, and processing stage if 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 moisture/dry-basis correction is required.
What You Receive
Clients receive a detailed Certificate of Analysis (COA) suitable for material valuation, refining decision-making, and process monitoring.
Your COA includes:
- Nickel and cobalt grade (wt%)
- Full impurity panel (Fe, Mn, Mg, Ca, 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 directly inform material valuation or refining decisions.
Methods & Standards
Sterling Analytical applies established methods adapted for MHP and related laterite-processing intermediates:
- EPA 3052 – Microwave-assisted acid digestion
- SW-846 6010 – ICP-OES elemental analysis
- Calibration using certified reference materials (CRMs)
Related Services
Explore related services:
- Nickel, Cobalt & Manganese Sulfate Analysis
- Nickel & Cobalt Concentrate Assay
- Black Mass Analysis
- Recycled Lithium Salt Analysis
- Iron Ore & Manganese Ore Analysis
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Frequently Asked Questions
It's used to verify nickel and cobalt grade and quantify the iron, manganese, and magnesium impurity content that determines MHP quality and refining requirements, supporting material valuation, refining decisions, and process monitoring.
Iron is typically the largest impurity by mass in MHP, carried over from incomplete upstream iron removal during HPAL processing. Elevated iron adds cost and complexity to downstream refining and can indicate an upstream process issue worth investigating.
MSP is the main alternative HPAL intermediate, typically higher in nickel grade (around 55%) but produced using hazardous hydrogen sulfide gas. MHP runs at lower grade with higher impurity load but has gained acceptance because it processes through the same refining equipment used for nickel briquettes, powder, or oxide. The two aren't directly comparable on raw grade alone since they reflect different precipitation chemistry.
MHP has emerged as an increasingly important nickel source for battery applications, processed differently from traditional sulfide-derived Class 1 nickel but capable of being refined into equivalent battery-grade material. Comparing impurity profiles between sources is relevant for sourcing and refining decisions.
Manganese co-precipitates with nickel and cobalt through an oxidative mechanism distinct from straightforward hydroxide precipitation, making it sensitive to precipitation conditions in ways that aren't always intuitive from pH alone.
10–20 grams of representative MHP, typically as wet or dried filter cake.
Standard turnaround is 3–5 business days, with 24–48 hour rush service available.
Yes, where known. This helps with interpreting results relative to a dry-basis specification, since wet filter cake moisture content can vary and affects how grade percentages should be read.
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