Precipitated calcium carbonate is a byproduct of the sugar industry, produced during the purification of sugar from beets.
This waste has long presented a management problem for sugar producers. As many are discovering, however, by pelletizing precipitated calcium carbonate, they are able to recover value from what would otherwise incur waste management fees, instead offering it to the agriculture industry for use as a soil amendment or fertilizer input.
The following covers what led the industry to this point, the many benefits of using precipitated calcium carbonate in agriculture, and the process of pelletizing the material.
Managing Precipitated Calcium Carbonate Waste
Precipitated calcium carbonate, or PCC, is known by a host of names:
- Spent lime
- Carbonation lime mud
- Carbonation lime residue (CLR)
- Defecosaturation mud
- Beet lime
- Sugar beet lime
- Sugar beet processing lime waste
- Defacation lime
No matter what it’s called, though, the byproduct, produced in hundreds of thousands of tons every year, represents the same issues to sugar beet processors: waste management costs and potential liabilities.
PCC has traditionally been stored in stockpiles adjacent to the beet processing facility. These piles not only take up a significant amount of space, but the fine particle size of the material means it can become windblown when dry, potentially presenting risks to the surrounding area and ecology. Further, the piles grow weeds and become community eyesores.
These factors, combined with the growing pressure to build a more circular economy, have led sugar producers and others in waste management to look for alternative options for the waste.
Reusing Precipitated Calcium Carbonate (PCC) in Agriculture
Researchers have explored numerous beneficial reuse opportunities for precipitated calcium carbonate from the sugar industry, with some success. Most notably, they have focused on use in the cement industry, as well as a few others, but the material’s potential agronomic value is what scientists keep coming back to. The material can bring several benefits when used as an agricultural input:
Ph Adjustment
Researchers have found that as a form of lime, precipitated calcium carbonate can bring the same benefit to soils as more traditional forms of lime, namely by adjusting soil pH.
Lime has long been used by the agriculture industry to reduce the acidity of soils and increase the soil pH for optimal crop growth. And though slightly less effective than traditional sources of lime, PCC lime has been shown to be of excellent purity and high reactivity, making it ideal for use in adjusting soil pH.¹ PCC lime is also available at a much lower cost.
PCC has the potential to do more than simply adjust soil pH, though; it offers a few additional advantages as well:
Added Nutrients
In addition to adjusting soil pH, precipitated calcium carbonate also contains value in the form of agronomic nutrients. Similar to traditional lime, this includes calcium, but can also include several others. Nutrient content varies across sugar beet plants, but may also contain:²
- Nitrogen (N)
- Potassium (K)
- Phosphorus (P)
- Zinc (Zn)
- Copper (Cu)
These added nutrients mean that PCC could also serve as a complex fertilizer.
Root Rot Reduction
Precipitated calcium carbonate has also been shown to reduce the occurrence of certain types of root rot-causing actors in some crops.
In the production of field peas, for example, one study illustrated that a significant reduction in root rot severity for certain pathogens could be achieved with the application of PCC.³
In another study, PCC was shown to reduce root rot caused by Aphanomyces in sugar beets, a problem for which there is currently no other resolution apart from developing more resistant plant varieties.4
Pelletizing: The Answer to Reusing Precipitated Calcium Carbonate
While precipitated calcium carbonate could in theory be applied to fields as-is, it has historically not been utilized, because it is difficult to transport, meter, store, and accurately apply in its existing form.5
By pelletizing the PCC, either on its own or as part of another nutrient formulation, the material is transformed into an acceptable agricultural product, meeting the specific handling and application requirements demanded by the market. PCC also tends to be readily responsive to pelletizing as well, though some forms may be more difficult than others, depending on their chemical makeup.
Pelletizing precipitated calcium carbonate gives sugar producers the opportunity to derive value from their waste, potentially adding a new source of revenue, mitigating waste management costs, and developing a more environmentally sustainable approach to resource utilization in the process.
What is Pelletizing?
Pelletizing, also known as wet granulation, is a type of agitation agglomeration in which fines are tumbled in the presence of a binder to form agglomerates, which, through continued tumbling, continue to collect fines and grow until they reach the desired size.
Precipitated Calcium Carbonate Pelletizing Equipment
As with traditional limestone, pelletizing precipitated calcium carbonate can be carried out using a variety of agitation agglomeration equipment, including disc pelletizers (pan granulators), granulation drums, and pin mixers, or a combination thereof. The most commonly employed approach is the pin mixer – disc pelletizer combination.
A summary of each type of equipment is available below. For a more detailed explanation of the pelletizing process, see our article on limestone pelletizing.
Pre-Drying Precipitated Calcium Carbonate
The pelletizing process requires feedstock to fall within a specific moisture range, unique to each and every material. As precipitated calcium carbonate typically has a moisture content too high for pelletizing as-is, a pre-drying step is typically carried out in a rotary dryer. This prepares the feedstock for optimal pellet formation.
Pin Mixer
The pin mixer is a continuous, horizontal-type mixer that can serve as a standalone agglomeration device, or as a preconditioning device prior to a disc pelletizer. The pin mixer thoroughly mixes liquid and solid feed components to yield a homogeneous blend, and if desirable, small agglomerates or seed pellets (nuclei). The pin mixer accomplishes this through an intense spinning action.
The addition of a pin mixer to a disc pelletizing operation is well recognized for the many benefits it can offer to limestone pelletizing lines.
Disc Pelletizer
The disc pelletizer, also known as a pan granulator, is another type of agitation agglomeration equipment used to pelletize limestone. The disc pelletizer works by tumbling fines in the presence of a binder on a rotating disc.
As mentioned, while the disc pelletizer can be used as a standalone agglomeration device, it is frequently combined with the pin mixer to produce an efficient operation that yields a high-quality product.
The disc pelletizer is favored for operations looking for tight size control over particles.
Granulation Drums
Though less common, the granulation drum, or rotary drum, can also be employed for pelletizing precipitated calcium carbonate. The granulation drum tumbles PCC fines in a rotating drum as a spray system mounted in the drum distributes the binding agent.
The granulation drum is favored for its high throughput and simple operation.
Developing a Precipitated Calcium Carbonate Pelletizing Process
The variation across sources of precipitated calcium carbonate, combined with the need to meet the agriculture industry’s product expectations, can be a challenge for sugar producers looking to reuse their PCC.
FEECO recommends sugar producers go through feasibility and process development testing in a facility such as the FEECO Innovation Center to first gain a familiarity with how their specific source of PCC responds to pelletizing, and then to establish basic process criteria.
The Innovation Center offers capabilities for testing at both batch and pilot scale, on a single piece of equipment, or in combination. Once basic process parameters have been identified, testing can move on to continuous testing, incorporating drying and recycle for a complete picture of the process.
This approach to testing not only determines whether or not it is feasible to pelletize the specific source of PCC to the desired specification, but it also establishes the process conditions necessary to do so on a commercial scale.
FEECO then uses the data gathered during testing to engineer and build custom pelletizing equipment. Combined with startup and parts and service support, this gives sugar producers the assistance they need in bringing their pelletized calcium carbonate product to market.
Conclusion
As sugar producers continue to struggle with the management challenges associated with precipitated calcium carbonate, the many benefits of PCC as a soil amendment are becoming more attractive. Many sugar producers are discovering that the pelletizing process lends an ideal solution to their woes, mitigating waste management issues and providing a value-added product in return.
FEECO has been the industry authority on pelletizing limestone and other bulk solids since 1951. We offer the ideal testing environment for bringing ideas to life and engineering the custom equipment needed to build an efficient process that yields the desired results. For more information on testing services, custom pelletizing equipment, or parts and service support, contact us today!