With raw material costs increasing and the ever-volatile logistical costs, wouldn't it be nice to have a source for these materials in your own back yard? In the business of making cement, gypsum costs usually range form $15 to $35 per ton. Using synthetic gypsum can dramatically reduce these costs as well as provide other manufacturing, environmental, and political benefits.

Sources The two main sources of synthetic gypsum are power utilities and acid neutralization. Many electric power utilities use high-sulfur bituminous coal as their source of fuel.

To effectively reduce the problem of sulfur gases entering the atmosphere, U.S. Congress implemented the Clean Air Act in 1990, thus putting stringent restrictions on sulfur oxide emissions. The power utilities, in an effort to become compliant with this law, must now either use a high-cost, low-sulfur coal or scrub the flue gases.

There are a few different scrubbing media that are used. The most popular is lime or limestone. In this process, when the slurry is precipitated, it results in a byproduct known as Flue Gas Desulfurization (FGD) material, or synthetic gypsum. This is a very fine material and can have moisture ranging from 10% to 15% after a dewatering process. This combination makes the material difficult to handle, thereby denying the cement manufacturers the benefits of traditional gypsum systems.

The second source of synthetic gypsum is acid neutralization. The sulfate production of TiO2, used as a white colorant in many retail products, yields byproduct gypsum in the process of neutralizing acidic waste. The chemical gypsum produced is of high quality, but it also is fine and wet, making it difficult handle.

Overview In many cases, synthetic gypsum is available to cement producers at a lower cost than natural gypsum. Typically, FGD forms of synthetic gypsum are extremely hard to handle due to the sticky nature of this material in wet form.

There are reported cases where cement producers have conducted cement production trials using a blend of FGD synthetic gypsum and natural gypsum. These trials yielded marginal success as difficulties were encountered in feeding the blended material through a conventional silo. Other cases exist where cement producers have utilized FGD synthetic gypsum as a 100% replacement for natural gypsum with proven success. In these cases, the key to success is having the ability to feed and accurately meter the FGD material.

Quality-Comparisons have been made of the quality parameters for initial set, false set, early and late strength gain of Type I and Type II cements produced with 100% FGD gypsum versus cements produced with 100% natural gypsum. The results show no variation in the cements produced and reveal no impact on cement performance.

Process-FGD gypsum in wet form can benefit the cement grinding process by inducing inherent moisture into the mill, thus providing cooling that may otherwise be accomplished by use of a water spray system. As a result of this potential moisture introduction into the grinding process, gypsum dehydration is reduced by using FGD gypsum.

Environment-FGD gypsum in wet form can be stored in open stockpiles without environmental impact resulting from fugitive emissions. Forms of FGD gypsum produced from coal-fired boilers do not contain hazardous materials.

Cement manufacturers have tried various methods to use these materials but have failed in many cases. Companies, such as Bulk Materials International, offer the design, installation, and, if needed, financing of a turn-key system. As a testament to the success of this process, cement manufacturers like Essroc Cement's Nazareth plant, Allentown Cement, and Blue Circle's Harleyville plant have had success in handling synthetic gypsum.