Marine Minerals

Seawater is a dilute but remarkably well-ordered electrolyte. At a salinity of about 35, one kilogram carries roughly 10.8 g of sodium, 1.28 g of magnesium, 412 mg of calcium, 399 mg of potassium and 19.35 g of chloride, with sulfur at 898 mg as sulfate, strontium at 7.9 mg and lithium at 174 µg. The list keeps going well below the milligram line, and it keeps its proportions: iodine sits near 58 µg per kilogram, molybdenum near 10 µg, zinc below a single microgram. There are two ways to turn that into something you can weigh out. The first is to take the water away and let the salts crystallise in their natural order, halite first, then the potassium and magnesium salts that refiners leave behind as bittern. The second is to let an organism do the concentrating, and marine life is very good at it: an oyster laying down a shell that is 95 to 98% calcium carbonate, a cuttlefish building a chambered aragonite shield, a diatom casting a perforated silica box around itself, a fish storing apatite in its bones.

Both routes are on our list. We supply sea salt in unrefined and refined grades, calcium from shell, nacre and fish bone, magnesium salts recovered from bittern, marine fractions that carry iodine or zinc, multimineral and trace mineral blends built to a stated ratio, and biomineral materials where the crystal phase and the microstructure are the whole point. Nothing here is sold as a bulk commodity with a single number attached: each family is quoted on a sheet that names the basis, the elements and the method.

Where a marine mineral actually comes from · 01

It helps to separate the two production routes before comparing grades, because they fail in different ways and they are quoted on different terms. Evaporation products are defined by how far the crystallisation was allowed to run and what the mother liquor still holds. Biomineral products are defined by which organism made them and therefore by the phase, the morphology and the residual organic matrix. A sheet that only says “calcium carbonate 98%” is not telling you enough to choose between them.

Sea salt products · 02

Salt is the cheapest mineral in the sea and the easiest to get wrong. Refining removes almost everything except sodium chloride, and everything it removes ends up in the bittern, which is why a refined salt and an unrefined flake salt from the same coastline can differ by an order of magnitude in magnesium and calcium even though both are described as sea salt. We quote sodium chloride on a dry basis, moisture separately, water-insoluble matter, and the particle size distribution by sieve, and when a customer wants the unrefined profile we put the magnesium, calcium and potassium figures on the same sheet instead of leaving them as a footnote.

Coarse salt from a solar pond, still carrying the minor ions that refining takes out.

Chloride is the majority ion in seawater at roughly 55% of the dissolved salt by mass, sodium about 30.6%, sulfate 7.7%, magnesium 3.7%, calcium 1.2% and potassium 1.1%. A production run that stops early keeps a larger share of that minor fraction; a run that goes to high purity gives it all away. Which one you want depends on whether the sodium chloride is the product or just a by-product of getting at the rest.

Marine calcium ingredients · 03

The hard parts of marine animals are mineral first and biology second. Mollusc shells run 95 to 98% calcium carbonate, and the shell is not uniform: the oyster builds a rough prismatic outer layer in calcite, then a foliated or nacreous inner layer, with aragonite concentrated where the shell has to take load, at the hinge and the muscle attachment pads. Nacre itself is about 95% aragonite in stacked platelets roughly 10 to 20 µm across and about half a micrometre thick, glued by a few per cent of protein and chitin. That organic fraction is why nacre is tough and also why it has to be removed before any thermal conversion, or it burns off inside the kiln and takes the colour and the carbon content with it.

Shell opened to the nacre layer: aragonite platelets held by a thin organic matrix.

If you need the oxide rather than the carbonate, the phase decides the energy cost. Aragonitic material starts losing carbon dioxide from about 800 °C, calcite needs 850 to 1000 °C, and production runs are typically held between 750 and 950 °C for two to three hours. Oyster shell, being calcite, resists the aragonite to calcite recrystallisation that mussel shell and cuttlebone go through between roughly 250 and 500 °C, so the two are not interchangeable in a kiln schedule even though their analyses look alike.

Shell also carries a record of the water the animal filtered, and the tissue that is left on the shell is where that record is written: dried oysters analysed by ICP-MS have returned cadmium near 96 µg, lead near 59 µg and arsenic near 446 µg per 100 g. The heavy metals panel therefore travels on the same certificate as the calcium, and the particle size is quoted separately, because a shell powder sold as a filler and the same powder sold as a reagent are separated more by the metals line and the sieve cut than by the calcium figure.

Marine magnesium ingredients · 04

Magnesium is the second most abundant cation in seawater at about 1,290 mg per kilogram, and the practical source is not the sea directly but the brine that salt works and desalination plants leave behind. The classic seawater route precipitates magnesium hydroxide from the brine and converts it to the chloride; where potash is mined, the hexahydrate crystallises straight out of carnallite. Either way, the grade you buy is defined less by the magnesium figure than by the calcium and sulfate limits and by how the material behaves when it meets heat and humidity.

Bittern magnesium: flake material crystallised from salt mother liquor.

Two figures decide most complaints with this family. The first is solubility: the hexahydrate dissolves to about 167 g per 100 mL at 20 °C, which is convenient in solution but also means it pulls moisture out of the air quickly. The second is what happens above 95 °C, where the crystal water leaves and the material starts to hydrolyse, so an application that needs anhydrous magnesium chloride needs material that was never allowed to hold water in the first place, or a carbo-chlorination step, not a hotter oven.

Zinc-bearing marine ingredients · 05

Marine organisms accumulate metals from very dilute water, which is why shellfish are among the densest natural sources of zinc and why the same tissue also concentrates cadmium. That pairing is the whole conversation with this family: a zinc figure on its own is not enough, because the routing of the element through filter feeders means the cadmium travels with it.

We supply zinc-bearing fractions as the raw concentrates, with the zinc and the cadmium reported side by side on the same basis, and with the species and the harvest area named. If a project needs a defined zinc level rather than a tissue powder, the blend is built and then re-assayed, and it is that second assay that goes on the sheet.

Iodine-bearing marine ingredients · 06

Iodine is the trace element the sea gives away most unevenly, because brown seaweeds actively accumulate it rather than simply soaking it up. Laminaria digitata runs 0.3 to 1.1% of its dry matter as iodine, while Ascophyllum nodosum, growing on the same shore, stays between 0.01 and 0.1%. Analysis of Chinese kelp puts 0.13 to 0.69 g iodine per 100 g of dry kelp against an ash content of 19.35 to 45.29%, which is why the ash, not the dried blade, is the form most often traded.

Two practical points follow from the chemistry. Iodine is water soluble, and boiling kelp leaches essentially all of it into the water, so any wet processing step is a decision about where the iodine ends up rather than a neutral operation. It is also volatile at high temperature, so drying is done gently. And because the form matters as much as the total, we report how the iodine was determined and in which oxidation state it is carried, rather than a single figure with no method attached.

Multimineral ingredients · 07

A request for marine minerals in the plural usually means a blend, and a blend is only worth buying if the ratio is stated. We build them from bittern liquor, from evaporated seawater held at the source ratio, or from a solid composite of calcined shell and seaweed ash, and we report each element separately instead of one headline mineral percentage that hides where the mass actually sits.

Trace mineral ingredients · 08

The trace tier of seawater is where honesty about arithmetic matters most. Strontium sits at 7.9 mg per kilogram, lithium at 174 µg, iodine at 50 to 64 µg, molybdenum at 10.5 µg. Turning any of those into a percent of a saleable solid means moving an enormous mass of water, so we quote a concentration factor and a verified assay rather than implying the element is the bulk of the product.

Because a trace figure is meaningless without its basis, every trace mineral line we ship comes with the sample preparation stated, the instrument named and the limit of detection printed next to the result. If an element is below the limit of detection we say so rather than writing zero.

Marine biomineral materials · 09

Some customers are not buying calcium or silica at all, they are buying the architecture the organism arranged it into: layered, chambered, perforated, or in a phase that is metastable at room temperature. Nacre, cuttlebone, diatom frustules and fish bone apatite all belong in this group, and the specification that matters is the phase, the morphology and what is still left of the organic matrix.

Biosilica from diatoms: pale, chalky and full of the pores the frustule grew with.

Cuttlebone split open, showing the fine chambered aragonite septa.

Phase is the field that separates a good biomineral sheet from a decorative one. Aragonite is metastable, so it converts to calcite on heating somewhere between roughly 250 and 500 °C depending on the species, the water content and how the sample was dried. A supplier who names the phase is also telling you how much energy the conversion step will take, and whether a powder dried at 120 °C will still be the material that was tested at the start of the project.

Reading the certificate · 10

Mineral sheets disagree with each other more often than they are wrong, and the cause is usually the basis rather than the chemistry. A calcium figure on a dry basis and the same material reported as-is can differ by the moisture it picked up in transit; a carbonate figure and an oxide figure for the same powder describe different products. So we print the basis, the method and the detection limit next to the number.

The plasma torch of an ICP-OES, the instrument behind most of the element lines we quote.

Storage, humidity and heat · 11

• Magnesium chloride is deliquescent. It takes water from ordinary air until it dissolves in its own brine, so it belongs in a lined pack and a dry store, not in an open drum on a quay.
• Salt cakes. The mechanism is moisture cycling rather than weight, so an anticaking agent or a controlled-humidity store fixes a problem that a bigger bag does not.
• Calcium oxide slakes. Once it has taken up water it is no longer the material on the sheet, so the pack is opened as late as possible and resealed properly.
• Magnesium hydroxide carbonates slowly in air. Where a defined hydroxide content matters, the interval between opening and use is part of the specification.
• Aragonite is sensitive to heat and to hot drying. If the phase is the reason for the purchase, the drying temperature is a process parameter rather than a detail.
• Iodine is volatile above moderate temperatures and water soluble at any temperature. Kelp fractions are dried gently and kept dry, and any aqueous step is planned around where the iodine will end up.
• Salt dust is not harmless to equipment. Chloride dust pits austenitic stainless steel, so conveying and weighing areas are cleaned on a schedule rather than on inspection.

Where these minerals are used · 12

Matching a mineral to your process · 13

Very little of what we ship leaves as it arrived. Shell powder is sieved to a cut that suits the customer's blender, calcined to the level the downstream step needs, or converted to apatite where a phosphate is wanted rather than a carbonate. Bittern is diluted or further evaporated to hit an element ratio, and blends are re-assayed after mixing rather than calculated on paper.

• Grade and phase selection, including calcite, aragonite, hydroxide, oxide and apatite forms.
• Particle size cuts by sieve or by milling, with the distribution reported rather than a single mesh figure.
• Element ratio adjustment for blends, confirmed by a second assay after mixing.
• Calcination level specified as a temperature and a hold time, not as a colour.
• Heavy metals panel and a per-element certificate with method and detection limit.
• Packaging in bags, lined drums or bulk, with the humidity protection the material needs.

Send us the element list, the basis you want the numbers reported on, and the phase if the phase matters, and we will quote against that rather than against a generic grade.

For Research or Industrial Raw Materials, Not For Personal Medical Use!