Ferrate Capabilities

Ferrate both disinfects and coagulates drinking water or wastewater. Comparisons of  (FeO₄^2- )  treatment to conventional (chlorine + alum or ferric coagulants) have been made_, and the results show: 1) for drinking water treatment, Ferrate can remove 10–20% more UV₂₅₄ absorbance and DOC than ferric coagulants for the same dose, and the THMFP was reduced to less than 100 μg /L by Ferrate at a low dose, 2) Ferrate can easily achieve the disinfection targets e.g. >6 log₁₀ inactivation of Escherichia coliform at a very low dose (6 mg/L) in comparison with chlorination, that required 10 mg/L  plus the ferric coagulant at 4 mg/L. In wastewater treatment, Ferrate can reduce 30% more COD, and kill 3 log₁₀ more bacteria compared to alum or ferric coagulants. Because of the small doses of Ferrate needed for treatment, less sludge is formed.

Also, it has been demonstrated that Ferrate acts as a dual-function chemical reagent (i.e., oxidant and coagulant) for drinking-water treatment, and performs better than ferric sulphate at lower doses for treating upland colored water. Ferrate can effectively remove natural organic matter and turbidity, and kills total coliforms (100%) at very low doses. In addition, under optimal study conditions, residual iron concentration and trihalomethane formation potential (THMFP) of Ferrate treated water fall below that of drinking water standards.

Ferrate has been shown to simultaneously remove both heavy metals (Cu, Mn, and Zn) and natural organic matter from river water.  Removal efficiencies range from 28–99% for Cu, 22–73% for Mn, and 18–100% for Zn at very low Ferrate doses. A high efficiency was achieved on the simultaneous treatment of heavy metals and NOM (10 mg/l): 87–100% (Cu), 31–81% (Mn), 11–100% (Zn), and 33–86% (NOM).

Ferrate has been shown to achieve removal efficiencies of 68 selected endocrine disrupting chemicals (EDCs), pharmaceuticals and personal care products (PPCPs) in secondary effluents of two wastewater treatment plants (WWTPs).  Thirty-one target EDCs and PPCPs were detected in the effluents of the two WWTPs with concentrations ranging from 0.2 ± 0.1 ng L⁻¹ to 1156 ± 182 ng L⁻¹. Fe(VI) treatment resulted in further elimination of the detected EDCs and PPCPs during Fe(VI) treatment of the secondary wastewater effluents. The results from this study clearly demonstrated the effectiveness of Fe(VI) treatment as a tertiary treatment technology for a broad spectrum of micropollutants in wastewater.

Study results have shown that ferrate and ozone pre-oxidation were comparable at equivalent doses for most DBP precursor removal. A net decrease in trihalomethane (THM), dihaloacetic acid (DHAA), trihaloacetic acid (THAA), and dihaloacetonitrile (DHAN) yield, while an increase in chloropicrin (CP) yield, were caused by both pre-oxidants. Ozone led to higher formation potentials of haloketones (HKs) and CP than ferrate at the same mass dose. In continuous flow experiments, the use of Fe(VI) pre-oxidation resulted in improved finished water quality as measured by UV absorbance, turbidity and DBPFP compared to waters with no pre-oxidation, or those pre-oxidized with Mn(VII).

A cyanide-laden effluent of the gold mining industry must be treated before it can be released to the aquatic environment. Current treatment methods such as natural degradation, sulfur based, hydrogen peroxide, ozonation, and alkaline chlorination are not adequate for meeting newer treatment standards. A new chemical oxidant that utilizes iron in the +6 oxidation state, ferrate [Fe(VI)] was studied to oxidize cyanides in gold mill wastewater. Reactions of cyanide and thiocyanate with Fe(VI) were analyzed to determine kinetic parameters, stoichiometry, and products. The complete removal of cyanide and thiocyanate can be achieved in seconds to minutes with the formation of less harmful products. Destruction of cyanide resulted in cyanate while sulfate and cyanate were the products of thiocyanate oxidation. Ferrate is therefore a suitable candidate as a new environmental friendly oxidant for gold mining wastewater.

The disinfection rate of ferrate(IV) was shown to be faster than that of chlorine at the same concentration. The effect of ferrate(VI) supplementation on coagulation of phosphorus was examined and compared with other common coagulants. Ferrate(VI) reduced more than 80% of total phosphorous in the range of doses between 5 and 25 mg-Fe/L.

Wastewaters containing americium and plutonium were treated with potassium ferrate and results showed that ferrate lowered the gross alpha activity from 3.0 × 10⁶ pCi/L to 6 000 pCi/L. An optimum treatment pH of 11.5 to 12.0 was found. At a Department of Energy (DOE) Facility demonstration, potassium ferrate treatment lowered gross alpha activity from 37 000 pCi/L to 40 pCi/L utilizing a two-step treatment process. The tests performed demonstrated that using potassium ferrate in the aqueous treatment plant at the DOE facility instead of the current treatment chemicals would ensure treatment requirements and that discharge limits are met.