Acidic wastewater rich in sulphur is a by-product of galvanic processing and the cleaning of flue gases at the power plants . However, the major producer of such wastewater runoff is the mining industry. Such effluents naturally cause a threat to the environment due to high concentrations of toxic and trace metals. The main cause is the constant oxidation of iron in pyrite ore as well as in the other sulphide minerals resulting from their exposure to the oxygenated water during mining and processing of coals and precious metals . Two remediation methods are known for this type of water normally called acid mine drainage (AMD). These include abiotic and biological technologies. Each system comprises two processes, namely, active and passive treatments. The active treatment method uses energy during the process of air pumping through the AMD and lime addition rendering it to be expensive while passive treatment is a new technology working without the requirement of mechanical equipment, electrical power, hazardous chemicals, or buildings, daily maintenance and operation. They are also more aesthetic and natural in their appearance and may support wildlife and plants. They involve using anoxic limestone and sulphatereducing bacteria or both to precipitate metals and neutralize acidity. These systems are sometimes described as bioreactors or wetlands. All these advantages make it less expensive compared to active treatment method has been chosen by the Bureau of Land Management . In this study, a new active treatment process was used to remove metals such as Iron and to neutralize the acidity of AMD using in-situ liquid sodium ferrate (VI) without using energy during the oxidation process and lime to neutralize the acidity. Oxidizing reagents such as ozone, free radicals, chromate and permanganate salts have also been used to remove it from wastewater and mine water as ferric hydroxide through precipitation process. Biologically, compost bioreactors, packed bed-iron oxidation bioreactors and permeable reactive barriers are frequently used to remove metals from AMD as passive systems . However, different studies have been conducted to remove or recover heavy metals such as Fe from water using passive and active methods, but no research was conducted to evaluate the settleability, quantity and composition of the sludge formed during its oxidation . In this regard, a vertical flow reactor (VFR) technique i.e., measuring cylinder in this study, which works under aerobic conditions to oxidize Fe 2+ from wastewater and water has been proposed to be applied for monitoring the sludge settling rate during its oxidation by sodium ferrate (VI). The removal of Fe 2+ in the earlier VFR systems was performed by precipitation of Fe (III) minerals, heterogeneous oxidation of Fe 2+ by ferrate (VI) ions and filtration of ferric hydroxides that are produced in the water column . The effectiveness of sludge settling depends on many factors, for instance, hydrodynamics and settling behavior of the sludge. This settling behavior depends on the flocculation tendency of suspended solids and sludge concentration throughout the system . Accordingly, four classes during settling can be illustrated including the discrete settling regime, discrete flocculent settling, hindered settling, and compression phase . This paper aims at exploring the removal of Fe 2+ by sodium ferrate (VI) as an eco-friendly emerging water treatment oxidant without filtration, studying and characterizing the sludge settling rate formed in a VFR system at a low pH value.