**5.1 Active technologies for the treatment of AMD**

The appropriate strategy used to mitigate wastewater (acidic) that includes the expansion of a chemically neutralizing agent is known as active treatment. The addition of various basic materials will improve the pH and accelerate the oxidation process (chemical) of (Fe2+) and precipitation of different metals into hydroxide and carbonates. The different neutralizing agents viz. lime, slaked lime,

**Figure 7.** *Common neutralizing reagents.*

sodium-carbonate/hydroxide, calcium/magnesium-carbonate/hydroxide can be utilized which is shown in **Figure 7**; differ in cost and efficiency. Although active chemical treatment has better efficiency for mitigation of AMD water, it has a disadvantage of high operational cost and produces more amount of sludge as an effluent. In this treatment process a variety of refinements to improve its efficiency and minimizes the sludge-related problems. The different flocculating reagent is added to increase precipitation. The iron-rich sludge created by the expansion of basic material is highly voluminous and rich in water. This sludge is used as a recycling process by dewatering the sludge in a lime-holding tank [19].

The cost for AMD treatment depends on the location and different scenarios like requirements of manpower, mechanical equipment, and dispensing facilities, and also cost. Soda ash, caustic soda, and ammonia have the lowest cost due to the less expensive equipment needed for the operation. Calcium oxide has the highest cost of installation because of the construction of a lime treatment plant and an aerator. The calcium hydroxide cost is low but the operation cost is high which is used for a long period of treatment for high loading and high acidic condition. Different active technology method which are generally followed for the treatment of AMD is given in **Table 2**.


**Table 2.** *Different active treatment technology.* *Performance Evaluation of Waste Materials for the Treatment of Acid Mine Drainage… DOI: http://dx.doi.org/10.5772/intechopen.99669*
