"The bulk of the body of knowledge on phosphatic clays has come about as a result of FIPR's research. One prime example is a long term study FIPR funded that produced the multi-volume "Evaluation of Phosphatic Clay Disposal and Reclamation Methods" series. Out of this research also came the SLURRY model that is the tool regulators and the industry use in mine planning for clay settling areas. The model estimates the consolidation rate of the clay and the capacity of the pond. It has become the industry standard tool. It is so commonly used that it is like the paint on the wall."

Stephen Partney
Administrator
Florida Department of Environmental Protection
Bureau of Mine Reclamation
On: FIPR's phosphatic clay research

Clay is part of the matrix that phosphate companies mine. The matrix contains roughly equal parts of sand, clay and phosphate. The finest particles of clay, sand and phosphate are separated in cyclones during the first stages of beneficiation. They are suspended in a watery slurry, commonly called phosphatic clays, and pumped to large impoundment areas for natural settling. The slurry is from 3% - 5% solids when it is pumped to a pond. As it settles, the clear top water is recycled for use in the beneficiation plant. Through research, methods have been developed to hasten the settling so that a top crust forms in 3-5 years after the start of dewatering and reclamation. Beneath the crust, however, the clay is still the consistency of pudding. After several years the clay settling areas are only about 25% solids.

A FIPR research focus has always been to try to understand phosphatic clays. FIPR has funded research to improve the impoundment areas where the clays are stored, understand how these areas impact the region's hydrology, evaluate the settling areas' impact on public and environmental health, and find ways to reclaim and use these areas as well as ways to use the clay.

Recently, concerns raised in communities where phosphate companies are trying to permit new mines have heightened the focus on phosphatic clays. Residents in communities to the south worry that the settling areas, which take up 40% of the land that has been mined, will adversely impact the local hydrology and that they will change the way the land can be used.

"Part of my job is to find solutions," said Karen Lulf, Engineering Manager for Mining Operations with Cargill Crop Nutrition, adding that FIPR has helped her. "When you are out there looking for solutions, the first thing you do is look at what's been done in the past. The FIPR library," she added, "has an impressive amount and variety of information on what has been done and it is readily available in one place. That information is valuable. You never know what bits and pieces of past research may be applicable today."

"I rely heavily on FIPR research when it comes to industry wide problems," she continued. "Pond (process) water and clay, for instance, are issues every company faces. We may work on them independently, but as an industry we have to share the information we have and solve such problems together. FIPR's information is for everyone."

FIPR research has shown these settling areas to be rich agricultural soil, but harder and more costly to farm than conventional land during the wet season. The land is also not well suited for development because of its limited load-bearing capacity. Structures built on clay settling areas need to be built on pilings to provide proper support.

Hardee County, which has traditional clay settling areas and areas of sand-clay mix reclamation sites, is now concerned that the land is of limited use because of its load-bearing capacity. Some sand-clay mix reclamation was done because the county opted about 25 years ago to have CF Industries use it in their county for agricultural purposes.

Public concerns have refocused the interest on research having to do with the clay associated with phosphate mining and finding alternatives for dewatering and use. FIPR has hosted a series of workshops for the industry and area mining community leaders to discuss what is known about the clay and what research needs to be done. The 2003 Florida Legislature even set aside $800,000 for FIPR to conduct a bench- and pilot-scale study of a clay dewatering process it has developed to determine its technical and economic feasibility.

Following are current FIPR projects related to phosphatic clays and the settling areas where they are stored:

• FIPR-DIPR
  

  FIPR is developing bench- and pilot-scale studies with special funding from the Florida Legislature to determine the technical and economic feasibility of a process FIPR has developed that rapidly dewaters the clay associated with phosphate mining. The value of such a process would be to decrease the amount of land used to store the watery clays and/or thicken the clay enough to use for immediate reclamation of mine cuts, as a lightweight aggregate, or for other purposes yet to be defined.

  The process that will be tested is known as the FIPR/DIPR. DIPR is an acronym for De-watering Instantaneously with Pulp Recycle. The process involves flocculating the phosphatic clay with a polymer, strengthening the flocs with a fibrous material such as waste paper pulp or sewage sludge, and separating the flocs from the water by screening or hydrocyclone. It was developed in the early 1990s. It has not been used because earlier studies conducted by phosphate companies estimated the process would be more expensive than the current method of clay disposal.

  Today, however, there are new considerations that may be changing the feasibility of using the FIPR/DIPR process. Those in the industry who deal with the phosphatic clays say that the cost of building the dams and reclaiming the ponds must be factored into the cost of the process and could change the way the industry looks at the FIPR-DIPR process cost.

• Deep Cone® Paste Thickening
  

  FIPR is also funding another promising technology designated as Deep Cone® Paste Thickening for rapid dewatering of clay and reclamation of mine cuts. Mechanical thickening is widely used for dewatering mining tailings as well as for clarifying water. A typical thickener is a large tank with a cone-shaped bottom section and a slow-moving rake. Before flocculants were introduced, thickeners were short and wide, and occupied large areas, achieving slow settling. Addition of a flocculant in the traditional thickener can speed up settling and achieve higher solids, but it took the smaller area E-Duc® Flocculation to realize high-rate thickening for ultra-fine particles. The Deep Cone™ Paste Thickener, evolved from the high efficiency E-Duc® thickener, is a super-efficient thickening technology that produces a high-solids paste rather than a slurry.

• Wetlands on Clay Settling Areas
  

  Clay settling areas (CSAs) contain wetlands but there is an ongoing debate about whether such wetlands can be reestablished as ecologically functional wetlands that can replace wetlands disturbed or destroyed in the mining process. There are more than 100,000 acres of CSAs in Florida.

• Hydrology of Clay Settling Areas

The public has expressed concerns about the possible impacts of clay settling areas on surface and groundwater systems. Downstream users of the Peace River have been especially concerned about possible mining effects on stream flows.

To try to answer some questions concerning phosphate mining impacts on the area hydrology, FIPR is funding a study that focuses on the effects that clay settling areas have, if any, on surrounding surface and groundwater flow.

Do they add to or detract from the surface and groundwater flow in their watershed?

Soils on reclaimed clay settling areas have a lower permeability than Florida's natural sandy soils. It was once believed that water might not infiltrate into the soil, and there would be greater runoff and flooding potential. This led to an early emphasis on CSA designs that would reduce peak discharges and prevent flooding. Excessive discharge, however, proved not to be a problem because as CSA soils dry they crack, allowing water to sink in. Further, as the clays consolidate, the surface of the settling areas subside, creating depressions that hold water.

Concerns for clay settling areas have thus shifted from flood prevention to providing adequate surface discharge and groundwater recharge to sustain stream flows.

It is important to be able to understand and predict internal and external hydrologic relations. The internal CSA hydrology is related to supporting wetlands and the external hydrology is related to impacts on surface and groundwater systems in the region.

This project proposes to determine the complete water balance of a CSA and proposes methodology for more accurate determination of how much water is lost to evaporation and how much groundwater seepage there is.

While progress has been made in improving the ability to predict clay consolidation and account for it in modeling CSA hydrology, there are still uncertainties in making accurate estimates of evapotranspiration and groundwater seepage.

Results from the FIPR study will likely be included in a broader study the Southwest Florida Water Management District (SWFWMD) is conducting of phosphate mining and other impacts on the Peace River Basin.

• Commercial Tree Crops
  

  Underutilized reclaimed phosphate mined lands in Polk County are crucial to the maintenance and expansion of commercial forestry in central Florida. FIPR is funding a project to identify, develop, and/or document superior trees, appropriate management practices for cypress, cottonwood and slash pine commercial tree crops, the productivities of superior genotypes, and their economic value on clay settling areas and overburden sites.

  As of September 2003, the study was showing that the main problem with establishing trees on a clay settling area was the trees' ability to compete with the invasive, non-native cogongrass that covers the settling areas. While previous research showed slash pine grew well as an ornamental tree on clay settling areas, this work is showing pine that grows more slowly than the cottonwood or cypress and is more susceptible to cogongrass competition. Slash pine was, however, performing well on overburden. As for cottonwood and cypress, the study is showing that when cogongrass is controlled, cottonwood is more productive than cypress although the cypress grows well.

  Nonnative eucalyptus trees being grown in related, non-FIPR, research were the most productive and competed better with the cogongrass.

• Related Research Features (Links)
  
  
  • Using clay settling areas to produce an alternative public water supply
    

    Almost a decade of research sponsored by the Florida Institute of Phosphate Research has produced a system that uses mined land to clean surface water well enough to meet drinking water standards and potentially be pumped into the aquifer, which would act as a natural storage reservoir and pipeline, allowing the water to be pumped out at the point where it is needed.

  • Using phosphatic clay to control red tides
    

    Estimates of Florida red tides vary considerably, but costs of $20 million dollars for episodes that last several months are often cited. Scientists are working on ways of stopping red tide. One possible solution is being studied at the Woods Hole Oceanographic Institute with Florida Institute of Phosphate Research (FIPR) funding. This project is indicating that the clay phosphate mining leaves behind could be used to stem Florida red tide.