Grantee Research Project Results
Final Report: The Use of Sludge Generated by the Neutralization of Acid Mine Drainage in the Cement Industry
EPA Contract Number: EPD06021Title: The Use of Sludge Generated by the Neutralization of Acid Mine Drainage in the Cement Industry
Investigators: Silsbee, Michael
Small Business: RJ Lee Group, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2006 through September 30, 2006
Project Amount: $69,961
RFA: Small Business Innovation Research (SBIR) - Phase I (2006) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Small Business Innovation Research (SBIR)
Description:
Acid mine drainage (AMD) is the outflow of acidic water from mining areas where pyrite and other sulfide minerals are exposed during mining operations. Once exposed to oxygen and water, the pyrite decomposes into a mixture of iron hydroxide and sulfuric acid. The resultant acid lowers the pH of waterways and often kills virtually all aquatic life. Although the most effective way of dealing with AMD is to prevent its formation, in many cases prevention is not feasible. In some cases, the AMD is neutralized with an alkaline agent such as caustic soda, hydrated lime, quick lime, or alkaline byproduct such as limestone dust. As the AMD is neutralized, an iron-rich floc is formed. In most active treatment systems, this floc is collected either in a clarifier or in sedimentation ponds, creating a sludge that require disposal. AMD sludge currently has no viable end use, and its disposal is costly. Therefore, a beneficial end use for the waste is highly desirable.
The goal of this study was to demonstrate the use of AMD treatment sludge as a viable component in the manufacturing of Portland cement. Portland cement is composed of a mixture of calcium, silicon, aluminum, and iron oxides. When AMD is dewatered, the resulting sludge is composed largely of calcium, iron, and aluminum hydroxides. Because calcium, iron, and aluminum are three of the four principal components of Portland cement, the use of AMD sludge as a feedstock for the manufacture of cement could have both economical and environmental benefits.
Summary/Accomplishments (Outputs/Outcomes):
AMD sludge was sampled from multiple treatment facilities across the State of Pennsylvania. Laboratory analyses were performed to determine the chemical composition of each sludge sample. To characterize the potential usefulness of the sludge in cement manufacturing, portions of AMD from the Brandy Camp active treatment facility in Clearfield County were fired with the raw materials used in the process of manufacturing Portland cement. The effects of additions at several different levels were studied.
In addition, mortar cubes were created for each of seven mix design ratios, where Portland Type I cement was replaced with AMD-derived product (sintered product). These mixtures were analyzed for compressive strength, Vicat setting time, and micro-structural analyses.
The results of this study demonstrate the technical viability of using AMD treatment sludge as feedstock for cement manufacture. Laboratory studies showed that, when added in appropriate amounts, the phase composition of the resulting cements did not change. Isothermal calorimetery results demonstrated that the hydration characteristics of the cements prepared using AMD remained relatively unchanged.
When sintered AMD was used as a partial replacement for Portland cement at levels of up to 10 percent, only a statistically insignificant decrease in strength was observed. The use of the sintered AMD also caused a small increase in the set time.
Conclusions:
The major hurdles to the widespread use of mining wastes as feedstock for cement manufacture are: (1) a natural hesitation on the part of the manufacturers to introduce a new variable into their system; and (2) economics. In Pennsylvania the economic variable is the calcium content of the conventional feedstocks, which are calcium poor. Adding increased amounts of an iron-rich feedstock would require the manufacturer to also add additional calcium—for which they may be paying a premium price.
The use of the sintered AMD as a partial replacement for Portland cement has intriguing potential. The sintering of the AMD occurs at a much lower temperature than the clinkering of cement, which means less energy consumption and lower emissions. Also, fewer carbonates are consumed, which reduces the release of CO2. The use of the mineral admixture also imparts a slightly darker color to the resulting mortar, creating interesting decorative applications.
In summary, the use of AMD in the cement industry is technologically feasible and economically marginal. Failing a strong incentive to change their practices, the use of AMD by the cement industry will grow only slowly.
Supplemental Keywords:
cement, mineral admixture, acid mine drainage, AMD, treatment sludge, small business, SBIR, Portland cement, mine waste, heavy metals, water reuse,calcium hydroxide, aluminum hydroxide, iron hydroxide, treatment byproducts,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Sustainable Industry/Business, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, pollution prevention, Environmental Engineering, waste treatment, sludge reuse, cement alternative, cleaner production, alternative products, environmental sustainability, alternative materials, active process control, environmentally benign alternativeThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.