Heavy metals (Cd, Pb, Zn, Ni, Cu and Cr(III)) removal from water in Malaysia: Post treatment by high quality limestone

Acid mine drainage control and treatment.

When appropriately designed and maintained, passive systems can provide long-term, efficient, and effective treatment for many acid mine drainage (AMD) sources. Passive AMD treatment relies on natural processes to neutralize acidity and to oxidize or reduce and precipitate metal contaminants. Passive treatment is most suitable for small to moderate AMD discharges of appropriate chemistry, but periodic inspection and maintenance plus eventual renovation are generally required. Passive treatment technologies can be separated into biological and geochemical types. Biological passive treatment technologies generally rely on bacterial activity, and may use organic matter to stimulate microbial sulfate reduction and to adsorb contaminants; constructed wetlands, vertical flow wetlands, and bioreactors are all examples. Geochemical systems place alkalinity-generating materials such as limestone in contact with AMD (direct treatment) or with fresh water up-gradient of the AMD. Most passive treatment systems employ multiple methods, often in series, to promote acid neutralization and oxidation and precipitation of the resulting metal flocs. Before selecting an appropriate treatment technology, the AMD conditions and chemistry must be characterized. Flow, acidity and alkalinity, metal, and dissolved oxygen concentrations are critical parameters. This paper reviews the current state of passive system technology development, provides results for various system types, and provides guidance for sizing and effective operation.

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Review of Passive Systems for Acid Mine Drainage Treatment

Limestone drains to increase pH and remove dissolved metals from acidic mine drainage

Trends in environmental variables are often investigated within a study region at more than one site. At each site, a trend analysis determines whether a trend has occurred. Yet often also of interest is whether a consistent trend is evident throughout the entire region. This paper adapts the Seasonal Kendall trend test to determine whether a consistent regional trend occurs in environmental variables.

Regional Kendall test for trend.

Much attention has been devoted to developing inexpensive, limestone-based systems for treating acid mine drainage (AMD) with little or no maintenance. Treatment of AMD with limestone results in a surface coating of metal hydroxides, a process known as limestone armoring. Once armored, limestone is assumed to cease dissolution and acid neutralization. Laboratory and field experiments determined acidity changes in AMD when contacted by armored and unarmored limestone and investigated the implications of armoring on the construction of open limestone channels for treating AMD. Results of a laboratory titration study indicated armored limestone was only 2 to 45% less effective in neutralizing a hydrochloric acid solution as unarmored limestone. A laboratory container study showed that armored limestone was 90% as effective in neutralizing AMD as unarmored limestone. The field study surveyed 2- to 8-yr-old, rock-lined channels constructed of sandstone or limestone, and measured water quality changes down the length of the channel. Open limestone channels, though armored, reduced more acidity in AMD (4-62%) than the sandstone channel (2%). The results from open limestone channels were compared to an acid neutralization kinetics model that predicts the rate of acid neutralization for a specified channel size, and AMD flow and acidity concentration. The open limestone channels in the field neutralized more acidity than the model predicted. Open limestone channels show promise for neutralizing AMD in watershed restoration projects and abandoned mine land (AML) reclamation projects where one-time installation costs are incurred, little to no maintenance is required, and systems do not have to meet specific water quality standards.

Acid Mine Drainage Treatment with Armored Limestone in Open Limestone Channels

Acid mine drainage (AMD) is often associated with mining of pyritic coal and metal deposits. Typical AMD associated with coal mines in the eastern US can have acidity and iron concentrations ranging from the teens to the thousands of mg/l. Aluminum and manganese can be present in concentrations ranging from zero to the low hundreds of mg/l. Much attention has been devoted to developing inexpensive, limestone (LS)-based systems for treating AMID with little or no maintenance. However, LS tends to coat with metal hydroxides when exposed to AMID in an oxidized state, a process known as {open_quotes}armoring{close_quotes}. It is generally assumed that once armored, LS ceases to neutralize acid. Another problem is that the hydroxides tend to settle into plug the pore spaces in LS beds forcing water to move around rather than through the LS. While both are caused by the precipitation of metal hydroxides, armoring and plugging are two different problems. Plugging of LS pores can be avoided by maintaining a high flushing rate through the LS bed. Armoring, however, occurs regardless of water velocity. This study investigated the influence of armoring on LS solubility and the implications of armoring and plugging on the construction of open (oxidizing)more » LS channels for treating AMD. We evaluated the AMID treatment performance of armored and unarmored LS in oxidizing environments both in laboratory and field studies.« less

D. L. Brant

Papers

Acid Mine Drainage Treatment with Armored Limestone in Open Limestone Channels

Acid mine treatment with open limestone channels