One of Vermiculite’s most peculiar characteristic is its ability to expand when exposed to the presence of a naked flame. The expansion occurs in an orthogonal direction from the plane of the laminar cleavage (flaking) mono-dimensionally without any variation in the ultimate area size.
The name exfoliation derives from the expansion process, which the Vermiculite platelets undergo during heating. The best way to describe the physical process is to compare it to the opening of an accordion’s bellows. The most likely cause of the exfoliation is the mechanical effect caused by the aqueous vapour, in which the crystallised water is instantaneously transformed at very high temperatures. However it is also believed that the expansion is due to severe arching of the platelets under the severe heat stresses generate by a flame.
LAF use a gas fuelled vertical vortex furnace where the vermiculite ore is introduced 2-3 m above the flame. The ore falls through gravity against the flow of hot gases towards the flame. As the product exfoliates, it changes its physical aspect, and it’s fall is arrested by the increased resistance offered by the rising heat. As the material exfoliation (expansion) continues, the product’s direction is inverted and it begins to rise due to the furnace exhaust suction. It is then collected in large tanks and allowed to cool.
Vermiculite through exfoliation undergoes deep changes which differentiate the exfoliated product from its ore state. Chemically speaking the major change is the loss of water of crystallisation and the inevitable crystalline mutation. The loss of crystalline water is irreversible even after immersion in water for months. The pH is also changed with a slight shift to alkaline given that the agnesium impurities which at high temperatures transform into oxides.
A lot more remarkable are the changes that occur in its physical state. The colour changes are more or less proportional to the amount of iron present in the chemical composition and where it oxidises to various degrees. The consequence of overheating the Vermiculite can give rise to the total dehydration of the particles resulting in a silvery tone colour. On the other hand low heating will result in poor exfoliation with brown or the original colours showing in patches.
The fundamental characteristic of the Vermiculite is its low specific weight which it acquires through the process of exfoliation. The most important parameter when wanting to adjudicate any commercial importance to a Vermiculite ore is its exfoliation rate. The average volume weigh of exfoliated vermiculite varies from 60 to 300 kg/m³.
This ample field of variability is due to more than just the ore type but also from the different methodologies of weighing the exfoliated product by the many manufacturers whom follow local scientific laboratory methodologies. The weights can be recorded immediately after exfoliation or left for a period to rest in the laboratory. It is a known fact that Vermiculite can increase in weight by as much as 10% within the first 24 hours after exfoliation after which weigh gain becomes irrelevant. Furthermore the volume weight of exfoliated vermiculite can be determined by the filling of known volume containers with or without settlement or vibration.
Exfoliated vermiculite can be easily compressed. It is logical to assume that after long periods of storage (in factory or on site) and through transport stages, the volume of the exfoliated material will reduce. As soon as the heating slows and the exfoliated vermiculite begins cool the volumetric expansion of the vermiculite granule will slow. As the vermiculite cools its volume will also decrease. On average this is 7% for coarse and medium grades and 5-6% for the finer grades.
As stated through bag palletisation and settlement vibration, storage and transport play an incredibly important part in the volume reduction of exfoliated vermiculite, on average the storage reduction can be quantified as follows:
- 4.5% volume loss for coarse grades:
- 3.1% volume loss for medium grades;
- 1.2% volume loss for fine grades:
The above volume reduction figures have been derived from bags collected from the bottom of the pallet approximately 15 days after being placed in storage.
Naturally the volume loss through transportation will be more severe as the length of travel and number of transhipments increase. The loss of volume for a one off 800 km rail shipment, was quantified as follows:
- 10% volume loss for coarse grades:
- 9% volume loss for medium grades;
- 7% volume loss for fine grades:
These volume reductions are to be taken as maximum values as rail transport can be considered as the roughest transportation method in use.
Another fundamental characteristic of exfoliated vermiculite is its very low thermal conductivity. Thermal conductivity is known as the heat that passes through 1 m² of wall 1 m thick and where the temperature difference between each side of the wall is one degree centigrade. The Thermal conductivity of exfoliated vermiculite at different temperatures is as follows:
For more information on Vermiculite, go to this link: www.ExfoliatedVermiculite.com
LAF manufactures vermiculite for use in growing medium products, professional growers and nurseries. With over 50 years of trading LAF has a high level understanding of what our user needs and how to best nurture supplier/user relationships. We place great emphasis on understanding the required product quality and the level of service the user demands. Like many of our horticultural vermiculite users, we choose our suppliers very carefully. We adhere to our customer’s order schedules, and we always deliver on the specified time or earlier.
LAF’s production is focused on standard industry vermiculite grades equivalent to superfine (1), fine(2) and medium (3). All materials are sampled and tested by our quality control laboratory in accordance with our Quality Assurance procedures conforming to ISO 9001 quality standards. The testing includes sieve analysis and bulk density determination. LAF collect all data and we are always aware of the degree of natural product variability.
LAF supplies exfoliated vermiculite to professional growers and nurseries in NSW. Our growers are demanding and always quick to point our product variation even when this is based on a visual comparison from that used previously. As a result, our vermiculite must be as uniform as possible. From the customer’s perspective, a number of issues must be kept in mind when considering vermiculite. Occasionally, the presence of ‘fines’ gives the impression that a finer grade of Vermiculite may have been mixed with another. LAF do not mix ores from different sources. However over the years we have learnt that ores have fluctuations in ore particle size distributions. As a result our customers perceive that the product might have been contaminated with finer vermiculite or that it is simply different from what they expected.
Discoloration is another cosmetic problem that is often raised where the tone of the vermiculite product changes within the same batch. In some cases, growers using our Vermigro product might attribute germination or plant growth problems to the fact that the growing medium as ''different" from the previous batch.
Variation in exfoliated vermiculite bulk density is another annoying problem that, the user often refers to when inferring poor quality control management by the supplier. An increase in specific weight can signify that the product was partially expanded or in the worst case scenario, that the ore was too fine.
When used as a growing medium, excessively fine vermiculite has been known to cause some complications to plant growth. Superfine vermiculite is known to retain excessive amounts of water after irrigation, thus resulting in cultural problems in the greenhouse. For this reason, bag to bag particle size distribution (PSD) consistency is of paramount importance. In the same way vermiculite sizing may also have an effect on plant growth.
As producers of horticultural grade vermiculite, we go to great lengths to ensure the material is uniform from bag to bag, pallet to pallet and year to year. All of these checks and balances allow us to manufacture a more consistent product which our customers have come expect, over the last 50 years.
Since 1960 LAF have worked with suppliers to provide our clients with the highest quality products they seek, whilst keeping material and labour costs down. To achieve this, we continuously search the world over for vermiculite ore suppliers that are prepared to work with us and our customers.
LAF manufacturing facilities have sufficient storage capacity to accommodate up to five 40ft HC shipping containers at any one time.
The raw material is received at our factory in bulk-a-bags and stored in our undercover production area. The material to be processed in one day is emptied into a holding hopper (Hopper 1) and from there it is elevated by bucket elevator to holding hopper (Hopper 2) at the top of the plant. From there the material is extracted via a variable speed auger and gravity fed into the vertical furnace. Upon coming into contact with the gas flames the material expands, and is then transported by suction back into a dust collector at the top of the building. Here the material collected at the bottom and through a rotary valve discharged into Exfoliate holding hoppers (E/Hoppers 1-4).
Every bag holds 100 litres and this is pre-determined volumetrically at the bagging plant. The bags are then palletised with 24 bags per pallet (1150 x 1150 mm). To further reduce handling costs LAF have introduced a 1000 litre bulk-a-bag with a further capacity to supply in jumbo bags (2,000 litre bulk-a-bag) if required.
In order to pass on further cost savings from reduced landfill tipping fees LAF have worked with preferred customers on a bag recycling scheme. LAF have always been pro-active in advising our customers if a delivery is being delayed, or if there is a problem, we deal with it quickly and professionally.
LAF stays in regular contact with our customers. Over the years, our unswerving customer focus and product quality have forged many lasting business relationships .