Formation/Geology
Ball clays were formed by a natural chemical process of super heated steam issuing from the hot interior of the earth through fissures in its granite crust causing decomposed feldspars in the granite to form kaolinite. This process is known as hydrothermal alteration. The difference between ball clays and china clays or kaolins is that the former was washed out of the parent granite by the natural action of rivers and streams and subsequently deposited in sedimentary lenses. The most popular theory regarding the formation of ball clays in the USA states that these deposits were formed by sedimentation along the eastern edge of the Mississippi embayment. These deposits were formed in a time when the region was tropical in climate and largely a swampy region.

History of USA Ball Clays and Commerce
Ball clays have been located in the USA, primarily, in Tennessee, Kentucky, Mississippi, Texas, California and Maryland with the largest and purest deposits in Tennessee and Kentucky. The highest concentration of commercial mineral development has occurred in Henry and Weakley counties of Tennessee and Graves County, Kentucky. In this region typical clay deposits are 20 acres in size with a clay depth of between 18 and 40 feet.

In the case of Old Hickory Clay Company, there are 13 active mines between the two states. The normal deposit consists of three grades of clay, with the most organic on top, the purest clay in the middle and the most silicious clay at the bottom. A deposit will have 25 to 80 feet of overburden which is normally sand, lignite and/or gravel.

The development of USA ball clays in this region began in 1860 in Tennessee and as early as 1880 in Kentucky. The first commercial clays shipped out of state were sold 100 years ago in 1894. By WWII, the use of domestic ball clays began to see real growth. By 1979, the ball clay industry was producing over 900,000 tons annually for industrial users worldwide.
Presently, there are four ball clay companies which mine and process ball clays from the Tennessee and Kentucky area: Old Hickory Clay Company, H.C. Spinks Clay Company, Kentucky Tennessee Clay Company, United Clays, Inc. (WBB).

Ball Clay Production
Deposits of clay are secured by land purchase or mineral lease by the clay company, after a sufficient and a successful exploration effort. Permits are obtained to develop mine at the chosen site. At this time, also a reclamation plan has been developed for returning the land to good and fertile condition. A drilling crew conducts confirmation core sampling prior to formulating a mining plan. A mining plan is developed based on the compilation and study of data received from the confirmation drilling. A stripping crew then removes the overburden necessary to retrieve the desired clay according to the mining plan. At this point, the site is carefully inspected by the production manager and mining superintendent to determine if the pit is ready for mining. If the site is ready, the mining crew is moved in to begin mining.

The mining crew conducts the most critical step in the entire clay production process; clay selection. This is also the first step of clay blending which will be addressed later. The mining superintendent, with the assistance of Quality Control lab and production manager, determines what to mine and what to question. As the clay is being mined, samples at the mine are being collected and tested by the Quality Control lab each hour or by specific request of the mining superintendent. The clay is transported by dump trucks to the PDF (Primary Drying Facility) at the plant sites, where the clay is stored for several months. Old Hickory Clay Company, has two plant sites - one in Hickory, KY which also is the site for its headquarters and research lab and one in Gleason, TN. Both sites have PDF's large enough to hold over 40,000 tons of clay.

Processing
Clay processing is performed in batch fashion with the true beginning being the receipt of an order. After an order is received written instructions are given to the production superintendent. These instructions delineate the specific quantity of each end-point clay used to produce the desired grade. The loader operator selects the desired crude end-point clays and then mixes them in a mixing bin. The mix is then shredded which further blends the clays. The shredded clay is then conveyed to one of the following process stages:

1. Finished grade storage
2. Mechanical drying process
3. Airfloating process
4. Slurry process

The clays are checked for applicable process control parameters by trained quality control technicians at each production stage. Samples of the finished product are collected and retained in the lab with the lot number recorded on each sample. This SPC data is entered into a computer database for each customer allowing the Quality Control manager to study a host of control variables for process and/or material trends. He also prints quarterly SPC reports for customers with several shipments each quarter. This provides valuable communication to the end user. The further processing stages are described as follows:
1. Shed-run shredded - naturally-dried clay from the PDF, processed through the clay shredder moisture range 12-22 percent. Processing: shredding (size reduction only)
2. Shredded and mechanically dried - shredded clay processed through fluid-bed dryers the moisture ranges: 11-16 percent, 8-13 percent, 5-10 percent
3. Airfloated - size reduced with limited beneficiation through a Raymond Imp mill (hamermill). Old Hickory Clay Company's method of processing is to flash dry while milling to achieve desired moisture. Moisture 0.05 - 3.5 percent. Processing size reduction is to very uniform material.
4. Slurried - The clay is blunged, screened and shipped with solids content between 60% and 64%. Deflocculant is added for dispersion and suspension characteristics. The slurry is aged in tanks and shipped in tank truckloads or private tank cars.

Blending
Blending is the most critical step. The end-point clays, which are stored separately in the PDF, are carefully selected and mixed. The mixed clays are then further blended in a shredder. Further blending stages occur in the finished product bins for shed-run shredded and mechanically dried clays, the airfloating process, and the slurry blunger and in-process tanks.

It is not a good practice to conduct grade selection with a drag line. Although this equipment is useful in the overburden removal step, it is not precise enough a tool for grade selection. The clay producer using a methodical quality-based plan for mining and production of ball clay products can achieve unsurpassed and constantly improved consistency.