Aragonite Natural Calcium Carbonate

What is Aragonite and Why is it found here?

The Bahamas has been a blessed nation in terms of its location in the sub-tropical region of the north-western hemisphere, its geological makeup being an archipelago is a string of islands strewn like pearls in shallow seas as it sits atop mountains of limestone made from coral almost as tall as Mount Everest.

These minerals are all the treasures of the sea and the living organisms within it, which are formed by natural processes that have taken millions of years to make. Some of the smallest animals in the sea are responsible for creating one of the highest mountain plateaus in the world on which this archipelago now sits. The bounty of these shallow seas is a wealth of pure minerals that is used in a lot of consumer products, almost too numerous to mention. Such as glass, paint, ceramics, jewelry and plastics just to name a few.

Oolitic Aragonite (which is the chemical name) is one of the purest forms of the Calcium Carbonate molecule that has a slightly different crystalline structure because of how it is made; it is referred as a Polymorph of that molecule. Oshenite, which is the commercial name of oolitic aragonite, is created by two other small living organisms, Plankton and Algae that freely swim in the seas. The seas around the isles of The Bahamas are already carbonate-rich and as these microscopic creatures feed on these minerals a purer form of limestone is produced; Oolitic Aragonite which falls like snow as a precipitate and accumulates on the ocean floor. This is the reason is mineral is everlasting, because it is being replenished by the living organisms in the shallow seas around these isles; where the food is plentiful and the sun aids in the production and regeneration.

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which is a type of sedimentary rock consisting mainly of calcite) and is the main component of pearls and the shells of marine organismssnails, and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous.

Occurrence

Calcite is the most stable polymorph of calcium carbonate. It is transparent to opaque. A transparent variety called Iceland spar (shown here) was used to create polarized light in the 19th century.

Geological sources]

Calcitearagonite and vaterite are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include limestonechalkmarble and travertine.

Biological sources

Calcium carbonate chunks from clamshell Eggshellssnail shells and most seashells are predominantly calcium carbonate and can be used as industrial sources of that chemical. Oyster shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source. Dark green vegetables such as broccoli and kale contain dietarily significant amounts of calcium carbonate, however, they are not practical as an industrial source.

Geology

Carbonate is found frequently in geologic settings and constitutes an enormous carbon reservoir. Calcium carbonate occurs as aragonitecalcite and dolomite as significant constituents of the calcium cycle. The carbonate minerals form the rock types: limestonechalkmarbletravertinetufa, and others.

In warm, clear tropical waters corals are more abundant than towards the poles where the waters are cold. Calcium carbonate contributors, including plankton (such as coccoliths and planktic foraminifera), coralline algaespongesbrachiopodsechinodermsbryozoa and mollusks, are typically found in shallow water environments where sunlight and filterable food are more abundant. Cold-water carbonates do exist at higher latitudes but have a very slow growth rate. The calcification processes are changed by ocean acidification.

Where the oceanic crust is subducted under a continental plate sediments will be carried down to warmer zones in the asthenosphere and lithosphere. Under these conditions calcium carbonate decomposes to produce carbon dioxide which, along with other gases, give rise to explosive volcanic eruptions.

Industrial applications

The main use of calcium carbonate is in the construction industry, either as a building material, or limestone aggregate for road building, as an ingredient of cement, or as the starting material for the preparation of builders’ lime by burning in a kiln. However, because of weathering mainly caused by acid rain, calcium carbonate (in limestone form) is no longer used for building purposes on its own, but only as a raw primary substance for building materials.

Calcium carbonate is also used in the purification of iron from iron ore in a blast furnace. The carbonate is calcined in situ to give calcium oxide, which forms a slag with various impurities present, and separates from the purified iron.

In the oil industry, calcium carbonate is added to drilling fluids as a formation-bridging and filtercake-sealing agent; it is also a weighting material which increases the density of drilling fluids to control the downhole pressure. Calcium carbonate is added to swimming pools, as a pH corrector for maintaining alkalinity and offsetting the acidic properties of the disinfectant agent.

It is also used as a raw material in the refining of sugar from sugar beet; it is calcined in a kiln with anthracite to produce calcium oxide and carbon dioxide. This burnt lime is then slaked in fresh water to produce a calcium hydroxide suspension for the precipitation of impurities in raw juice during carbonation.

Calcium carbonate in the form of chalk has traditionally been a major component of blackboard chalk. However, modern manufactured chalk is mostly gypsum, hydrated calcium sulfate CaSO4·2H2O. Calcium carbonate is a main source for growing Seacrete. Precipitated calcium carbonate (PCC), pre-dispersed in slurry form, is a common filler material for latex gloves with the aim of achieving maximum saving in material and production costs.

Fine ground calcium carbonate (GCC) is an essential ingredient in the microporous film used in diapers and some building films, as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching. GCC and PCC are used as a filler in paper because they are cheaper than wood fiber. In terms of market volume, GCC are the most important types of fillers currently used. Printing and writing paper can contain 10–20% calcium carbonate. In North America, calcium carbonate has begun to replace kaolin in the production of glossy paper. Europe has been practicing this as alkaline papermaking or acid-free papermaking for some decades. PCC used for paper filling and paper coatings is precipitated and prepared in a variety of shapes and sizes having characteristic narrow particle size distributions and equivalent spherical diameters of 0.4 to 3 micrometers.

Calcium carbonate is widely used as an extender in paints, in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble. It is also a popular filler in plastics. Some typical examples include around 15 to 20% loading of chalk in unplasticized polyvinyl chloride (uPVC) drainpipes, 5% to 15% loading of stearate-coated chalk or marble in uPVC window profile. PVC cables can use calcium carbonate at loadings of up to 70 phr (parts per hundred parts of resin) to improve mechanical properties (tensile strength and elongation) and electrical properties (volume resistivity). Polypropylene compounds are often filled with calcium carbonate to increase rigidity, a requirement that becomes important at high usage temperatures. Here the percentage is often 20–40%. It also routinely used as a filler in thermosetting resins (sheet and bulk molding compounds) and has also been mixed with ABS, and other ingredients, to form some types of compression molded “clay” poker chips. Precipitated calcium carbonate, made by dropping calcium oxide into water, is used by itself or with additives as a white paint, known as whitewashing.

Calcium carbonate is added to a wide range of trade and do it yourself adhesives, sealants, and decorating fillers. Ceramic tile adhesives typically contain 70% to 80% limestone. Decorating crack fillers contain similar levels of marble or dolomite. It is also mixed with putty in setting stained glass windows, and as a resist to prevent glass from sticking to kiln shelves when firing glazes and paints at high temperature.

In ceramic glaze applications, calcium carbonate is known as whiting, and is a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze. Ground calcium carbonate is an abrasive (both as scouring powder and as an ingredient of household scouring creams), in particular in its calcite form, which has the relatively low hardness level of 3 on the Mohs scale, and will therefore not scratch glass and most other ceramicsenamelbronzeiron, and steel, and have a moderate effect on softer metals like aluminium and copper. A paste made from calcium carbonate and deionized water can be used to clean tarnish on silver.

Health and dietary applications

500-milligram calcium supplements made from calcium carbonate

Calcium carbonate is widely used medicinally as an inexpensive dietary calcium supplement for gastric antacid (such as Tums). It may be used as a phosphate binder for the treatment of hyperphosphatemia (primarily in patients with chronic renal failure). It is also used in the pharmaceutical industry as an inert filler for tablets and other pharmaceuticals.

Calcium carbonate is used in the production of calcium oxide as well as toothpaste and has seen a resurgence as a food preservative and color retainer, when used in or with products such as organic apples.

Excess calcium from supplements, fortified food, and high-calcium diets can cause milk-alkali syndrome, which has serious toxicity and can be fatal. In 1915, Bertram Sippy introduced the “Sippy regimen” of hourly ingestion of milk and cream, and the gradual addition of eggs and cooked cereal, for 10 days, combined with alkaline powders, which provided symptomatic relief for peptic ulcer disease. Over the next several decades, the Sippy regimen resulted in renal failurealkalosis, and hypercalcaemia, mostly in men with peptic ulcer disease. These adverse effects were reversed when the regimen stopped, but it was fatal in some patients with protracted vomiting. Milk-alkali syndrome declined in men after effective treatments for peptic ulcer disease arose. Since the 1990s it has been most frequently reported in women taking calcium supplements above the recommended range of 1.2 to 1.5 grams daily, for prevention and treatment of osteoporosis, and is exacerbated by dehydration. Calcium has been added to over-the-counter products, which contributes to inadvertent excessive intake. Excessive calcium intake can lead to hypercalcemia, complications of which include vomiting, abdominal pain and altered mental status.

As a food additive it is designated E170, and it has an INS number of 170. Used as an acidity regulatoranticaking agentstabilizer or color it is approved for usage in the EU, USA and Australia and New Zealand. It is used in some soy milk and almond milk products as a source of dietary calcium; one study suggests that calcium carbonate might be as bioavailable as the calcium in cow’s milk. Calcium carbonate is also used as a firming agent in many canned and bottled vegetable products.

Agricultural use]

Agricultural lime, powdered chalk or limestone, is used as a cheap method for neutralising acidic soil, making it suitable for planting.

Household use

Calcium carbonate is a key ingredient in many household cleaning powders like Comet and is used as a scrubbing agent.

Environmental applications

In 1989, a researcher, Ken Simmons, introduced CaCO3 into the Whetstone Brook in Massachusetts. His hope was that the calcium carbonate would counter the acid in the stream from acid rain and save the trout that had ceased to spawn. Although his experiment was a success, it did increase the amount of aluminium ions in the area of the brook that was not treated with the limestone. This shows that CaCO3 can be added to neutralize the effects of acid rain in river ecosystems. Currently calcium carbonate is used to neutralize acidic conditions in both soil and water. Since the 1970s, such liming has been practiced on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly.

Calcium carbonate is also used in flue gas desulfurisation applications eliminating harmful SO2 and NO2 emissions from coal and other fossil fuels burnt in large fossil fuel power stations.

Precipitated Calcium Carbonate – Multifunctional Additive for PVC: Techno Brief

Calcium carbonate is one of the most widely utilized minerals. Ground calcium carbonates (GCC) are used mainly as fillers, while precipitated calcium carbonates (PCC), in addition to being reinforcing fillers, can function as a processing aids and impact modifiers as well. This Precipitated Calcium Carbonate guide is designed to help you understand more about the use of PCC in PVC polymer, focusing on the benefits and main applications.

Why use Precipitated Calcium Carbonate ?

Calcium carbonate have long been recognized as useful additives for thermoplastics and particularly in PVC for many applications. Ground calcium carbonate is generally used as a filler with an interesting ratio performance/price.

Precipitated Calcium Carbonate (PCC) however exhibits a much smaller particle size.

The specific structure and granulometry of PCC (see description) allows this materials to fulfill additional functions like Processing aidimpact modification and better weatherability.

Precipitated Calcium Carbonate is much more than a filler

Precipitated calcium carbonate is a versatile additive for use in a wide range of plastic and elastomeric applications. Its regular and controlled crystalline shape and ultrafine particle size together with the hydrophobic surface coating, combine to the benefit of both polymer processing and subsequent physical properties.

PCC is one of a unique class of additives which can be classified as being multi functional providing the end user with an outstanding cost/performance opportunity.

Precipitated Calcium Carbonate as Processing Aid – Article taken from the website of SpecialChem: The Material Selection Platform;  https://polymer-additives.specialchem.com/selection-guide/precipitated-calcium-carbonate

  • Introduction
  • Gelation time
  • Plate out elimination
  • Melt extensibility
  • Increased output
  • Surface finish 

                             

Introduction

When ultrafine CPCC is compounded into rigid PVC several quite specific effects are observed. Amongst those seen are:

  • Shorter fusion/gelation time.
  • Improved surface finish and gloss.
  • Elimination of plate out.
  • Elimination of surface defects, ie sharkskin which occurs under conditions of high shear gradients, such as those seen in injection molding operations.
  • These observed effects are usually associated more with the use of organic processing aids and impact modifiers than with the use of only an inorganic additive. 
  • However, the fact is that they are real effects seen with CPCC and clearly offer performance and economic benefits.
  •  
  • Gelation time
  • The degree of gelation is a measure of the breakdown of the PVC grain structure and its transformation into an homogeneous matrix. If the PVC is under gelled or over gelled, poor physical properties will result. CPCC, because of its very small particle size and surface coating generates fast, efficient fusion in PVC formulations. Comparison of Brabender (a fusion test) traces for a series of PVC mixes shows a fusion behavior for the CPCC containing mix having an almost identical trace to the traditional process aid. The GCC system has a markedly different profile (see figure 1).

The reason for this behavior is the compatibility of the CPCC primary particle size at ~70nm with the PVC primary particle. This compatibility allows good contact to develop which is instrumental in developing frictional heat. Because of the large number of CPCC particles present, this effect is distributed evenly throughout the PVC matrix. 

This results in more efficient heat up and ultimate fusion of the PVC granules, hence the earlier gelation. Electron micrograph studies of a series of dry blends based on both CPCC and a typical GCC clearly illustrate this point also (Table 1).

Table 1: CPCC / GCC comparison on dry blending behavior with PVC primary particles

Plate out elimination

Plate out is a phenomena sometimes observed during extrusion processes that has its origins in varying degrees of incompatibility within the formulation itself. This can involve lubricants and other additives used. The addition of acrylic process aids is known to improve this situation as a result of the enhanced fusion and improved compound compatibility that is promoted. 

Due to the ultrafine particle size of precipitated calcium carbonate and its ability to improve the state of dispersion of all the components present in such compounds, resistance to plate out is seen to improve when CPCC is included in these formulations. As a result of this running times can be extended without the need for costly delays in production for cleaning.

Melt extensibility

The resistance of a PVC melt to the applied shear forces during the various processing conditions that can be found in use, is a critical property for the polymer compound during its processing experience. This is particularly true for injection molding processes where the high shear gradients seen can give rise to surface defects which in some cases can be unacceptable and cause components to be rejected. Again conventional processing aids are often incorporated to improve the melt properties but also often can increase the melt viscosity and affect output potential

Benefits in injection molding

CPCC containing molding compounds demonstrate excellent processing behavior and produce components with high gloss without the need for conventional processing aids (see also surface finish). GCCs fail to match this performance even when used in combination with process aid. Table 2 illustrates the reformulation trends possible to optimise process aid in molding compounds. 

 

Formulation with process aid + GCC

Typical alternative
CPCC formulation

PVC

100

100

Stabiliser

2

2

Process aid

2

0

1µ GCC

3

CPCC

5

Table 2 The CPCC formulation represents a significant cost saving and features improved surface finish and lower reject rates.

Benefits in rigid PVC foam

The use of CPCC in rigid PVC foam formulations is seen to allow the development of a more regular and uniform cell structure (see figure 2). This property is derived from the beneficial improvement in melt reinforcement that accompanies the incorporation of these ultrafine calcium carbonates. Melt elasticity and elongation are improved which allows optimization in the use of other additives necessary for successful foam production. There has been speculation as to whether CPCC can act as a “nucleating” agent due to its very small particle size. This has yet to be confirmed although in theory this would be an expected outcome of their use.

                                   

with CPCC

 

without CPCC

Figure 2

Increased output

It is often desirable to maximize the production output but this can also be limited by the the speed of gelation of a PVC compound. 

While combinations of processing aids can be used in order to assist the fusion characteristics of a particular compound, precipitated calcium carbonate will allow high production output rates to be achieved without the need for such high usage of processing aids. This is of specific interest for larger output machinery where a suitable level of gelation has often been a limiting factor for high output.

Surface finish

CPCC containing compounds exhibit excellent gloss in extrusion and injection molding applications. In pigmented rigid PVC, CPCC gives an unparalleled degree of gloss as a consequence of its ultrafine particle size and absence of the large particles present in ground fillers that produce surface defects thereby increasing light reflection. Materials sometimes difficult to process such as CPVC (chlorinated polyvinyl chloride) are made more manageable if CPCC is included in the formulation. 

The photographs in figure 3 clearly show the smooth surface finish on the CPCC formulation compared to that with ground calcium carbonate.
The relatively large particles of the latter cause surface defects which increase light scattering.

Precipitated Calcium Carbonate as Reinforcer

The decisive advantage which results from the incorporation of ultrafine precipitated calcium carbonate in rigid PVC formulations relates to the significant improvement that is seen in the impact performance. This improvement is seen in rigid PVC compounds without the addition of any organic impact modifier. In the presence of both acrylic and CPE type modifiers, this improvement in the impact properties is repeated from the levels seen with the modifier alone. Whereas polymer modified compounds can display a sharp decrease in impact strength a low temperatures, the CPCC modified system possesses residual impact resistance even at low temperatures (see figure 1).

Figure 1: Mean height of fall h50 of roller blind profiles as a function
of Socal 312 content at varying test temperatures

In contrast to organic impact modifiers precipitated calcium carbonate increases the E modulus of the extruded component and increases the impact strength without reducing the rigidity. 

The explanation of this positive behavior can be found in both the processing improvements that synthetic calcium carbonate provides along with its ability to improve the dispersibility of other components of the formulation i.e. organic impact modifiers. This improved dispersion and processing benefit also results in the reduction on the % reversion observed for the extrusion of a typical window profile formulation (see table 1).

Formulation

% Reversion

Rate
m/min

single V Notch
Charpy impact at 23°C (kJ/m2)

 

TOP

BOTTOM

   

Ground filler system

1.87

2.02

1.1

14.0

Precipitated CC

1.57

1.67

1.1

hinge break

Table 1

The more complete gelation that results from the inclusion of precipitated calcium carbonate provides a matrix that in comparison to natural calcium carbonates has fewer defect sites and opportunities for a crack propagation process leading to reduced mechanical properties. The micrographs show the differences in failure mode for PVC containing precipitated calcium carbonate from those containing a natural calcium carbonate derived by milling (figure 2). It is possible to obtain ductile failures with reduced impact modifier levels by using precipitated calcium carbonate.

Figure 2

Other Applications of Precipitated Calcium Carbonate

Thermosets
Certain grades of PCC offer benefits in rheology control in polyester molding compounds where the bright color, positive effect on the viscosity and much improved surface finish and sandability are valuable property improvements.

Figures 1 and 2 show the particular effects that the fineness, the crystal structure and the free flowing density have on the viscosity of the polyester resins.

   

Figure 1: Influence of free flowing density of Socal® on viscosity and the yield value of mixtures Socal® Polyester (50:50)

Figure 2: Viscosity of mixtures Socal® /polyester (40:60) in the function of the mean diameter of Socal and the crystal structure

Liquid Resins in general
CPCC as a result of its ultrafine particle size and hydrophobic surface treatment will allow improvements in the control of the rheology in a range of liquid resin systems. The mechanism of effect results from the hydrophobic/hydrophilic balance of fatty surface treatment and the flocculated nature of the crystalline structures present in the product. Grades are easily dispersed in liquid system and the rheological effects do not require further addition of synergists or activators to be effective. Improved viscosity stability can be seen with time when compared to the use of other rheological control agents and CPCC presents fewer handling problems in use. 

Thermoplastics
In Polyolefins CPCC is used as an acid scavenger in the production and handling of various polyolefins. Beneficial properties are also seen in polyolefin compounding where low level addition of the high surface area grades will improve the anti blocking properties of thin film applications. 

Where injection moldings are produced from PE or PP, Socal® increases service temperature and gives the materials a high degree of brightness. The adding of 2 % to 4 % by weight makes PP film easier to splice while, at the same time, reducing PP deposits on fast-moving machine parts.

In polystyrene, the use of up to 30 per cent by weight of Socal® increases impact resistance, as well as reducing the use of TiO2

Free flow agent for powders
Coated ultrafine PCC acts to improve the flow properties of problem powders. The beneficial effect is seen when either the product is added into the final stages of a production stream as in the case of spray drying isolation or alternatively the CPCC can be added into a final product mix. The free flow and anti caking improvements seen require only 1-2% addition of the high surface area CPCC which helps to coat the surface of the bulk material reducing interparticle attractions. There is also a positive effect on the absorption of moisture from the particle interfaces, which also assists in the anti caking and free powder flow improvements observed. 

Liquid Carrier
The relatively high surface area of PCC can allow these products to be used as inert carriers for liquid catalysts. One example of this is where reactive organic peroxides can be absorbed onto the calcium carbonate allowing the production of an easy to handle catalyst paste for use in combination with reactive liquid resin components. The calcium carbonate has no adverse effect on any of the adhesion properties, which can be adversely affected by other thixotropic control agents.