A process for preparing ferric chloride for a water treatment process for producing potable water

Abstract

The invention relates to a process for preparing ferric chloride for a water treatment process for producing potable water comprising adding magnesium oxide to acid mine drainage (AMD) to produce a Fe(III) precipitate and a supernatant, (b) separating the Fe(III) precipitate from the supernatant, reacting hydrochloric acid with Fe(III) precipitate to produce ferric chloride rich solution, and using the ferric chloride rich solution in a water treatment process for producing potable water. The invention extends to a method for producing potable water using the ferric chloride rich solution produced according to the invention.

Description

[0001] A PROCESS FOR PREPARING FERRIC CHLORIDE FOR A WATER TREATMENT PROCESS FOR PRODUCING POTABLE WATER INTRODUCTION The invention relates to a process for preparing ferric chloride for a water treatment process for producing potable water. In particular, the process relates to the recovery of Fe(III) from Acid Mine Drainage and preparing ferric chloride from the produced Fe(III) to be used in a water treatment process for producing potable water. BACKGROUND OF THE INVENTION Climate change and rapid population growth, the latter of which is particularly concentrated in low and middle income countries (LMICs), are massively stressing the water and wastewater industry since both water consumption and wastewater generation are on the rise South Africa is one such example of an LMIC water demand and effectively treat corresponding wastewater quantities. Currently, South Africa is affected by water scarcity, with 60% of its rivers being overexploited and dam levels being dangerously low, while ~40% of its wastewater is released untreated further stressing freshwater quality (Zachary et al., 2018). To make things worse, a bio-recalcitrant wastewater matrix that greatly affects South Africa, and other countries with strong mining industries, is acid mine drainage (AMD), also known as acid rock drainage. AMD is highly acidic and typically contains elevated levels of iron (Fe), aluminium (Al), manganese (Mn), and sulfur (S), along with other traces such as heavy metals, rare earth metals, and even radionuclides (Masindi et al., 2022b). However, these contaminants, and particularly Fe and S, can render AMD a promising candidate for their recovery, e.g., as ferric sulfate (Fe2(SO4)3) (Kefeni et al., 2017, Naidu et al., 2019, Chen et al., 2021). Specifically, different beneficiation opportunities for AMD have been examined and the feasibility of recovering and producing sulfuric acid, gypsum, goethite, hematite, and magnetite has already been examined Fe(III) can be used to produce ferric-based coagulants, i.e., ferric salts such as ferric chloride (FeCl3) and Fe2(SO4)3, for water (Heddam, 2021) and wastewater (e.g., piggery (Lee et al., 2004) or municipal wastewater (Li et al., 2016)) treatment. Specifically, a typical water purification plant comprises screening, chemical dosing, sedimentation, filtration, and post chlorination. In chemical dosing, flocculants-coagulants, such as polyelectrolytes (water- soluble organic polymers) or ferric salts (typically FeCl3or Fe2(SO4)3) are employed (Zafra et al., 2020). Until recently, polymers were the preferred option in South Africa. However, after the 2022 Russian invasion of Ukraine, the supply chains for polymers were disrupted and the water and wastewater industry turned to ferric salts. This, in turn, led to iron coagulants cost and availability issues. As such, South Africa, and other sub-Saharan countries, currently struggle with the cost-effective procurement of iron coagulants. Raw AMD has been used as a coagulant for drinking water purification, due to its high Fe(III) content, but this was associated with many drawbacks since AMD itself is a wastewater matrix (Rao et al., 1992). The use of coal AMD has been also assessed for Al-based coagulant recovery and was found promising, but further research is required (Skoronski et al., 2016). The synthesis and recovery, at pH ≥ 5, 6, and 7, of poly-alumino-ferric sulfate (PAFS) coagulant from coal mine AMD, when using sodium hydroxide, has also been reported and found as efficient as commercially-available poly-ferric sulfate (PFS) for the treatment of brewery wastewater (Mwewa et al., 2019). Furthermore, PFS (Menezes and PAFS (Menezes et al., 2010) coagulants have also been and recovered, by selectively precipitating Fe and Al from coal mine AMD using sodium hydroxide at pH 3.8 and 5, respectively. These were then successfully used for raw (lake) water treatment, and, in both cases, the treated water met the Brazilian standards for drinking water quality (Menezes et al., 2009, Menezes et al., 2010). A need exists for an alternative source of Fe(III) to produce ferric chloride for treating water to render it potable. SUMMARY OF THE INVENTION An embodiment of the invention provides for a process for preparing ferric chloride for a water treatment process for producing potable water comprising: 1. adding magnesium oxide to acid mine drainage (AMD) to produce a Fe(III) precipitate and a supernatant, 2. separating the Fe(III) precipitate from the supernatant, 3. optionally, drying the Fe(III) precipitate, 4. reacting hydrochloric acid with Fe(III) precipitate to produce ferric chloride rich solution, 5. using the ferric chloride rich solution in a water treatment process for producing potable water. The pH after step 1 may be about 2.5 to about 4.5, preferably 3.5. The hydrochloric acid may be industrial grade hydrochloric acid, preferably the hydrochloric acid is present at a concentration of about 30%. Step 1 may occur by stirring in a mixer at a speed of between 300 rpm and 700 rpm, preferably between 400 rpm and 600 rpm, most preferably 500 rpm for between 20 to 50 minutes, preferably between 25 to 40 minutes, most preferably about 30 minutes. Further the resultant mixture of step 1 was left to equilibrate to allow the Fe(III) precipitate to separate from the supernatant in the mixture for between 15 minutes to 1 hour, preferably 20 minutes to 50 minutes, most preferably about 30 minutes. Step 2 typically occurs using a gravity filter or vacuum pump filter or gravity settling (from 10-60 minutes but preferably 30 minutes) due to density to separate Fe(III) precipitate from the supernatant. When step 3 is present, the Fe(III) precipitate may be oven dried at, preferably, 90 - 900oC, more preferably 95oC - 500oC, and most preferably 105oC for around 1 - 24 hours, more preferably 24 hrs. Step 4 typically occurs in a chlorination process to produce ferric chloride rich solution. In Step 5, the ratio of Fe(III) to water to be treated is in the ratio of 0.1 to 1 mL:L, preferably 0.1, 0.2. 0.4, 0.6, 0.8 or 1 mL:L, and most preferably 0.2 mL / L. The mixing step at step 5 is typically at a speed of 25, 50, 100, 150, 200 or 250 rpm, preferably 25 or 50 rpm and most preferably 100 rpm. The mixing time for contact between the ferric chloride and water to be treated is typically 1, 2.5, 5, 10, 15 or 30 mins, preferably 1 min, and most preferably 5 mins. The potable water may be left to settle for about between 30 to 120 minutes, preferably between 45 minutes to 90 minutes and most preferably 60 minutes. The potable water produced at step 5 have a pH in the range of between about 6 to 8, preferably 7.7 to about 8.1 and most preferably 7 and 7.9. Typically one or more of the following contaminants may be removed from the water to be treated in step 5 with ±10%: Al of about 99.8%, ammonia of about 99.8%, turbidity of about 99.7%, Fe of about 99.5%, Cr of about 99.2%, Ni of about 98.2%, COD of about 95.3%, Mn of about 92.9%, Cu of about 81.1%, Nitrite of about 67.6%, Nitrate of about 52%, colour of about 50%, Ca of about 48.8%, alkalinity of about 22.4%, Mg of about 11.8%, K of about 10.1%, Na of about 10%, sulfate of about 9.7%, EC of about 6.7% and pH of about 4.3%. The AMD may be prefiltered before adding magnesium oxide to remove suspended solids and debris from AMD and acquire pure AMD with chemical species in dissolved form for effective recovery of minerals of interest, in this case it is Fe(III). This will also aid in the removal of substances that could possibly contaminate or cross-contaminate the recovered Fe(III) from mine water or AMD hence impairing its purity and usability for ferric chloride production. Specifically, the solids and debris were removed by gravity filtration on the funnel, using Macherey-Nagel filter papers (in a range of MN 615. Ø125mm), and the filtered sample was immediately used for the recovery of Fe(III) from AMD prior subsequent steps. In another embodiment of the invention provides a method for producing potable water comprising using a ferric chloride rich solution in a water treatment process for producing potable water, wherein the ferric chloride rich solution is prepared using the following process: 1. adding magnesium oxide to acid mine drainage (AMD) to produce a Fe(III) precipitate and a supernatant, 2. separating the Fe(III) precipitate from the supernatant, 3. optionally, drying the Fe(III) precipitate, 4. reacting hydrochloric acid with Fe(III) precipitate to produce ferric chloride rich solution. The pH after step 1 may be about 2.5 to about 4.5, preferably 3.5. The hydrochloric acid may be industrial grade hydrochloric acid, preferably the hydrochloric acid is present at a concentration of about 30%. Step 1 may occur by stirring in a mixer at a speed of between 300 rpm and 700 rpm, preferably between 400 rpm and 600 rpm, most preferably 500 rpm for between 20 to 50 minutes, preferably between 25 to 40 minutes, most preferably about 30 minutes. Further the resultant mixture of step 1 was left to equilibrate to allow the Fe(III) precipitate to separate from the supernatant in the mixture for between 15 minutes to 1 hour, preferably 20 minutes to 50 minutes, most preferably about 30 minutes. Step 2 typically occurs using a gravity filter or vacuum pump filter or gravity settling (from 10-60 minutes but preferably 30 minutes) due to density to separate Fe(III) precipitate from the supernatant. When step 3 is present, the Fe(III) precipitate may be oven dried at, preferably, 90 - 900oC, more preferably 105oC for around 1 - 24 hours, more preferably 24 hrs. Step 4 typically occurs in a chlorination process to produce ferric chloride rich solution. The ratio of Fe(III) to water to be treated is in the ratio of 0.1 to 1 mL:L, preferably 0.1, 0.2. 0.4, 0.6, 0.8 or 1 mL:L, and most preferably 0.2 mL / L. The mixing step at step 5 is typically at a speed of 25, 50, 100, 150, 200 or 250 rpm, preferably 25 or 50 rpm and most preferably 100 rpm. The mixing time for contact between the ferric chloride is typically 1, 2.5, 5, 10, 15 or 30 mins, preferably 1 min, and most preferably 5 mins. The potable water may be left to settle for about between 30 to 120 minutes, preferably between 45 minutes to 90 minutes and most preferably 60 minutes. The potable water produced have a pH in the range of between about 6 to 8, preferably 7.7 to about 8.1 and most preferably 7 and 7.9. Typically one or more of the following contaminants may be removed from the water to be treated in step 5 with ±10%: Al of about 99.8%, ammonia of about 99.8%, turbidity of about 99.7%, Fe of about 99.5%, Cr of about 99.2%, Ni of about 98.2%, COD of about 95.3%, Mn of about 92.9%, Cu of about 81.1%, Nitrite of about 67.6%, Nitrate of about 52%, colour of about 50%, Ca of about 48.8%, alkalinity of about 22.4%, Mg of about 11.8%, K of about 10.1%, Na of about 10%, sulfate of about 9.7%, EC of about 6.7% and pH of about 4.3%. The AMD may be prefiltered before adding magnesium oxide. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an illustration of the embodiment of the invention in the form of integrated system for the recovery of Fe(III) along with the production of ferric chloride and clean water; Figure 2 shows contaminants / indicators percentage removal and pH variations in river water when treated with different dosages of a) AMD-synthesised FeCl3 and b) commercial FeCl3 (Conditions: 1 min mixing at 200 rpm, followed by 60 min settling time at ambient temperature and pH); Figure 3 shows contaminants / indicators percentage removal and pH variations in river water when treated at different mixing speeds for the a) AMD-synthesised FeCl3and b) commercial FeCl3(Conditions: 0.2 mL:L dosage and 1 min mixing followed by 60 min settling time at ambient temperature and pH); and Figure 4 shows contaminants / indicators percentage removal and pH variations in river water when treated for different contact times for the a) AMD-synthesised FeCl3and b) commercial FeCl3(Conditions: 0.2 mL:L dosage at 100 rpm mixing speed, followed by 60 min settling time at ambient temperature and pH). DESCRIPTION OF PREFERRED EMBODIMENTS Acid mine drainage (AMD) is a highly acidic wastewater matrix that is rich in dissolved metals and wreaks havoc into receiving environments. However, its high iron (Fe(III)) content presents an opportunity for recovery and use for iron salts production. Here, Fe(III) was selectively recovered from coal mine AMD, using magnesium oxide, and used for ferric chloride (FeCl3) production, a typical coagulant used in water and wastewater treatment. The present invention provides an alternative source of Fe(III) from AMD to produce ferric chloride for treating water that is cost effective and reduces the environmental impact of AMD. The present invention utilizes Fe(III) as a resource rather than a contaminant in AMD and this makes this approach more cheaper since conventional techniques are very expensive, sophisticated, and require more precursors than a direct recovery from mine water. The process used in the present invention further utilizes the Fe(III) from AMD to clean wastewater, this transforms the Fe(III) into a valuable resource in the water treatment process. This creates a sustainable solution and demonstrates its value as a strategic and economical viable solution for water treatment. The efficacies of both the AMD-synthesized and commercially available FeCl3were assessed for water and wastewater treatment and were found comparable. For river water treatment 0.2 mL / L (v / v ratio), 100 rpm of mixing speed, and 5 min of equilibration time suffice for its effective treatment and use for drinking water. This highlight that AMD-synthesized FeCl3can be safely employed by the water and wastewater industry in South Africa and further afield to address price and availability concerns surrounding commercial flocculants and coagulants. Furthermore, through AMD beneficiation, i.e., Fe(III) recovery, and partial acidity correction, water reclamation opportunities from AMD can be further pursued. Overall, resource recovery from waste and their reuse for treating other wastes can introduce sustainable paradigms and promote the United Nations (UN) sustainable development goals (SDGs). Even though Fe(III)-based coagulants can be synthesized and recovered from AMD, an important parameter that defines their properties is the alkaline material that is used for Fe(III) precipitation. Specifically, different alkaline materials can be used, including calcium (Ca) based materials such as limestone, lime, and hydrated lime and Du Plessis, 1993, Du Plessis and Maree, 1994, Geldenhuys 2003); magnesium (Mg) based materials, such as magnesite, periclase, brucite (Bologo et al., 2012, Masindi and sodium (Na) based materials, such as et al., 2017, Akinwekomi et al., However, when the selective recovery of Fe(III) is the sole target alkaline minerals are also associated with different drawbacks and disadvantages. For example, Ca-based materials have the tendency to co- precipitate Fe(III) along with other metals and sulfate , whereas Na-based materials exhibit high solubility and co- along with Fe(III) (Masindi and Tekere, 2020). Furthermore, Mg-based materials that contain high Ca concentrations can leads to gypsum formation, which cross-contaminates the Fe(III) sludge with sulfate (Masindi et al., 2022b). Nonetheless, Mg-based materials that contain relatively low Ca amounts are not associated with this drawback, since Mg and S have the tendency to complex towards magnesium sulfate (MgSO4(aq)), leaving Fe(III) to precipitate in a relatively pure phase (Masindi et al., 2018). In this regard, magnesite (Masindi et al., 2019) and magnesium oxide (MgO) derived from magnesite calcination (Navarro and Martínez da Matta, 2022) have already being used for metals removal from AMD, with the latter being more effective in AMD treatment Relatively pure Fe(III) has been also selectively when using MgO derived from calcined South African magnesite The present invention uses MgO obtained from South the selective recovery of Fe(III) from coal mine AMD. This was then used for ferric salt production, and specifically for FeCl3. FeCl3has been found to perform better in the present invention compared to Fe2(SO4)3 for water treatment applications, even at very low doses (Brandt et al., 2017). The present invention examines the efficacy of the AMD-synthesised FeCl3for the treatment water and wastewater treatment in the South Africa setting. This may open up opportunities for low-cost and readily available Fe(III)- based coagulants, thus also addressing water safety concerns in South Africa and further afield. The present invention relates to the recovery of Fe(III) from acid mine drainage via sequential recovery and its use for the production of ferric chloride for water treatment, a process of producing said Fe(III) for ferric chloride production and a method of the treatment of water with the use of ferric chloride. Referring to Figure 1, the process for producing AMD 12 and an alkali 14 (e.g. MgO) is added to a mixing vessel 16 to produce Fe(III) rich precipitate 18 and a supernatant 20. The Fe(III) rich precipitate 18 produced is reacted with HCl 32 in a vessel 34 to produce ferric chloride 36 and the ferric chloride 36 is stored in a container 38. Ferric chloride 40 is used to treat contaminated water 42 to render it potable. The supernatant 20 produced is sent for treatment in a vessel 22 for further treatment to remove residual metals and chemical species until clean water 24 that meets the discharge limit is disposed and contaminated sludge 26 is produced. The sludge will then be stored for further recovery of chemical species or disposed to the landfill. Reverse Osmosis could be coupled to the system to reclaim drinking water. 1 Materials and methods 1.1 Sample collection and reagents procurement Real AMD was collected from the coal heap (toe seep) of an active coal mine at Mpumalanga province, South Africa, using 25 L high density polyethylene (DHPE) containers (jerry cans). Before collection, AMD was pre-filtered using Macherey Nagel MN 615-Ø125 mm filter papers to remove debris and suspended solids and the filtrate was then moved and stored in the laboratory at 4°C, until use for Fe(III) recovery experiments. Raw water was collected from an abstraction point from Wilge River that feeds the water treatment plant of Gauteng Province, South Africa. Similarly, 25 L HDPE jerry cans were used for river water collection and the collected water was stored at the laboratory at 4°C, before being treated with FeCl3. Finally, municipal wastewater was collected from two wastewater treatment plants (P1 and P2) in Gauteng Province, South Africa. Again, municipal wastewater was collected using 25 L HDPE jerry cans, pre-filtered through Macherey Nagel MN 615-Ø125 mm filter papers, and stored at 4°C, before being treated with FeCl3. For Fe(III) selective precipitation and recovery from AMD MgO was used, which was produced by calcining locally available magnesite that was hand collected from a derelict magnesite mine in Folovhodwe, South Africa, as described elsewhere For FeCl3production from the recovered Fe(III) process was used. To this end, industrial grade hydrochloric acid (HCl) (30%) was procured from Sigma Aldrich and reacted with Fe(III), as described elsewhere (Almeida and Schneider, 2020). Finally, to assess the efficiency the AMD-synthesized FeCl3as a coagulant for water and wastewater treatment applications, its efficacy was identified and compared to the efficacy of commercially available FeCl3, when treating the same aqueous matrices. For this reason, commercially available FeCl3, which is already being used by South African water and wastewater industry, was procured from Protea chemicals (Pty) Ltd (43% FeCl3·6H2O). 1.2 Ferric iron recovery from AMD and ferric chloride synthesis For Fe(III) recovery from the coal mine AMD, selective precipitation, as described in (Masindi et al., 2018), was employed. Specifically, the pre- filtered AMD was transferred into a borosilicate laboratory reactor and was dosed with a predefined mass of MgO to increase the pH to 3.5, where Fe(III) grossly precipitates. Specifically, the AMD-MgO mixture was stirred for 30 min, at 500 rpm using an overhead stirrer, and was left to equilibrate for 30 min to separate the precipitate (Fe(III)-rich sludge) from the supernatant This pH value, i.e., 3.5, is fairly similar to the one the et al., 2009), i.e.3.8, to recover PFS from coal mine AMD when using NaOH. However, in our case study MgO was used instead of NaOH, which largely avoids the co-precipitation of sulfate. The precipitate was then oven dried (105 ℃ for 24 hours) and stored until utilization for FeCl3production. In order to synthesize FeCl3, the AMD recovered Fe(III)-rich sludge was reacted with industrial grade HCl towards FeCl3synthesis (AMD-synthesized FeCl3 thereafter). Specifically, following Almeida and Schneider (2020), 0.01 mol of HCl was added into a volumetric flask filled with deionised water to prepare a 0.001 M solution. Then, the Fe(III)-rich sludge was added and mixed, using a magnetic stirrer, for 30 min to synthesize FeCl3. Finally, 0.7 mL of the FeCl3-rich solution was added into a 1 L volumetric flask fill with deionised water to prepare the stock solution that was used in the coagulation studies. 1.3 Optimization studies Optimization studies were carried out to determine the optimum water treatment conditions when using the AMD-synthesized ferric salt (FeCl3). Specifically, the effect of FeCl3dosage, mixing speed, and contact time (mixing duration) on contaminants removal from the collected raw (river) water was examined. For this reason, batch experiments were conducted in the laboratory using the one-factor-at-a-time (OFAT) method. Specifically, changes in the pH were recorded, while the removal efficiencies (%) for Al, chromium (Cr), colour, copper (Cu), Fe, Mn, nickel (Ni), and zinc (Zn), among others, were calculated using Eq. (1):Removal (1)where Cinitialthe initial concentration of the examined contaminant / indicator and Cfinalthe final concentration of the examined contaminant / indicator. First, the effect of FeCl3dosage on contaminants removal was examined. To this end, six liquid to liquid (L:L) ratios, i.e., ferric salt to river water, were examined, ranging from as low as 0.1 to as high as 1 mL:L. Specifically, aliquots of the collected river water were added into six 1 L beakers and these were then spiked with defined volumes of the produced FeCl3to obtain the following L:L ratios: 0.1, 0.2, 0.4, 0.6, 0.8, and 1 mL:L. The mixtures were stirred for 1 min at 200 rpm in a jar test stirrer. Thereafter, the samples were afforded 60 min to equilibrate, as to allow time for the suspended solids to settle. The supernatant was then filtered using a Whatman gravity filter and the removal efficiencies were measured to identify the optimum coagulant dosage. Thence, using the optimum coagulant dosage the effect of mixing speed was examined. Specifically, the mixtures were stirred for 1 min using the following mixing speeds: 25, 50, 100, 150, 200 and 250 rpm, and similarly the quality of treated samples was assessed. Lastly, using the optimum dosage and mixing speed the effect of contact time was examined by considering the following mixing durations: 1, 2.5, 5, 10, 15, 30 min. In parallel, river water was also treated, at the exact same conditions, using commercially available FeCl3, as to be able to compare the efficacy of the AMD-synthesized FeCl3with its commercially available counterpart (commercial FeCl3 thereafter). Finally, the real water and wastewater matrices were treated with the AMD- synthesized FeCl3at the identified optimum conditions. For context, these matrices were also treated with the commercial FeCl3and the efficacy of both coagulants was compared. All experiments were performed in triplicate and results are reported as mean values. 1.4 Solid and aqueous samples characterization 1.4.1 Elemental composition of the Fe(III)-rich sludge recovered from AMD A detail characterization of both the MgO (and its parent material), as well as of the recovered Fe(III)-rich sludge can be found elsewhere (Masindi et al., 2018). The chemical composition of the recovered Fe(III)-rich sludge in the present invention provides insight about possible impurities in its matrix. The X-ray fluorescence (XRF) (Thermo Fisher ARL-9400 XP Sequential XRF equipped with Win-XRF software) analytical technique was employed. 1.4.2 Aqueous samples characterization For the characterization of the aqueous samples under study (raw and FeCl3treated water / wastewater) a multi-parameter probe (Hach Company HD40D) was used to measure the pH and electrical conductivity (EC). Turbidity was recorded using a tungsten lamp turbidimeter (Hach Company TL2350). Metal and non-metal fractions were determined using inductively coupled plasma mass spectrometry (ICP-MS) (Thermo Scientific XSERIES 2 ICP-MS, coupled to ASX-520 auto sampler) and inductively coupled plasma - optical emission spectrometry (ICP-OES) (Agilent Technologies 5110 ICP-OES coupled with SPS 4 auto sampler), as required based in their concentrations. 2 Results and discussion 2.1 Elemental composition of the recovered Fe(III) by XRF The elemental composition of the Fe(III)-rich sludge, which was selectively recovered from AMD and used for FeCl3production, is summarised in Table 1. As was expected, Fe(III) was the main constituent, by and large, while other elements, which were initially embedded in AMD, were also identified and they mainly include Al, Mg, Ca, and sulfate. The presence of Mg and Ca could be possibly traced back the alkaline agent (calcined South African magnesite) that was used for Fe(III) selective precipitation, whereas the remaining elements where likely co-precipitated along with Fe(III) from the AMD. Sulfate could be linked to gypsum and oxy-hydrosulfates formation, while Mn and Al are the linked to hydroxides, oxy-hydrosulfates, and potential carbonates during the recovery of Fe(III) from mine water (Michalková et al., 2013, Masindi, 2017, Nepfumbada et al., 2023). Notably, a high value for the high loss on ignition (LOI) was observed and this denotes the hydrous nature of the recovered material (Akinwekomi et al., 2020, Masindi et al., 2022a, Overall, the presence of Fe, but also Al, Mg, and Ca can be used for ferric salt production for water and wastewater treatment applications. Table 1: Elemental composition of the recovered Fe(III)-rich sludge that used for FeCl3production. Standard Real sample Recovered Analysed Certified standard sludge standard Element (wt.%) (wt.%) SiO2 49.94 49.82 1.96 Al2O3 13.8 14.26 2.27 MgO 7.23 7.82 5.36 Na2O 2.26 1.89 1.28 P2O50.273 0.34 0.11 Fe2O3 12.23 11.32 65.23 K2O 0.52 0.54 0.42 CaO 11.4 10.83 4.72 TiO22.71 2.54 0.05 V2O5 0.0566 0.06 0.01 Cr2O30.0422 0.04 0.01 MnO 0.168 0.17 0.10 NiO 0.0154 0.01 0.01 CuO 0.017 0.02 0.01 ZrO2 0.0242 0.03 0.04 SO-240.02 7.02 Co3O4 0.01 0.03 ZnO 0.01 0.01 SrO 0.12 0.23 Y2O30.05 0.01 BaO - 0.88 LOI 0.07 9.29 TOTAL 100.69 99.98 99.01 2.2 Optimization studies 2.2.1 Effect of ferric chloride dosage First, the effect of the AMD-synthesized FeCl3 dosage on river water treatment was examined. As mentioned above, L:L ratios in the range 0.1 to 1 mL:L (FeCl3 dosage to river water) were examined and the percentage (%) removals for turbidity, colour, Al, As, Cr, Cu, Fe, Mn, Ni, and Zn were estimated. To provide context and insight the same L:L ratios were also examined when using the commercial FeCl3. Results are shown in Figure 2. Regarding the AMD-synthesized FeCl3(Figure 2a), it was identified that even at the lower end of the examined ranged, i.e., 0.1 mL:L, turbidity, Al, Fe, Cr, and Mn have been practically removed (≥99% removal). The removal of Zn also plateaued, but the percentage removal was 50%. However, this is not an issue since the initial Zn concentration in the raw river water is many orders of magnitude lower than the ≤ 5 mg / L prescribed limit (SANS 241:2015) limit for drinking water. Colour removal optimizes at the next examined dosage (0.2 mL:L). Again, its percentage removal is only 25%, but similarly with Zn this is not an issue due its low initial concentration. Ni removal also optimizes at 0.2 mL:L dosage (98.5% removal), whereas As and Cu removal increases with increasing dosages and reaches 99.8% and 88.2% at the last examined dosage (1 mL:L), respectively. However, their concentration in the river water was below the SANS 241:2015 prescribed limit, and therefore, their removal efficiencies are not considered a limiting factor when examining the optimum coagulant dosage. As a result, it appears that the first examined dosage (0.1 mL:L) suffices for the removal of the contaminants of concern, i.e., turbidity, Fe, and Al, whereas the next examined dosage (0.2 mL:L) further optimizes the removal of most of the other contaminants and therefore can be considered as optimum. Finally, as was expected the pH of the treated water gradually decreased with increasing FeCl3 dosages, starting from pH 8.1 at the raw drinking water matrix to 7.7 at the last examined dosage (1 mL:L), since FeCl3 is acidic by nature. Similar results were obtained for the commercial FeCl3 (Figure 2b), with the main difference being that Fe is not practically removed at the first examined value, but its removal efficiency increases with increasing dosages. This is also the case for Mn, which percentage removal plateaus at a higher dosage (0.6 mL:L), when compared to the AMD-synthesized FeCl3. On the other hand, Ni removal optimizes at the first examined value, but colour achieves a lower removal efficiency. Nonetheless, Fe concentration greatly reduces at the first examined dosage (0.1 mL:L) and its concentration is lower than the recommended limit for drinking water, while Mn, Ni, and colour concentrations were below the recommended limit for drinking water. As such, both the AMD-synthesized and the commercial FeCl3have similar performances when used for river water treatment in the South African setting and in both cases the optimal coagulant dosage is 0.2 mL:L. The higher efficacy of the AMD-synthesized FeCl3in Fe and Mn removal is likely traced back to the small quantities of Mg and Al, since the presence of such cations is known to further improve the removal efficiency of Fe and particularly of Mn (Jones and Knocke, 2017). 2.2.2 Effect of mixing speed The effect of mixing speed on the percentage removal of the contaminants / indicators under study is shown in Figure 3. As mentioned above, six different mixing speeds were examined, i.e., 25, 50, 100, 150, 200, and 250 rpm. As shown in Figure 3a, when using the AMD-synthesized FeCl3, even at the lower end of the examined mixing speed, i.e., 25 rpm, the removal efficiencies for turbidity, Fe, Cr, Ni, and Al are very high (≥99%) and only slightly increase with increasing mixing speeds. Colour removal further increases at the next examined mixing speed, i.e., 50 rpm, and remains stable up to the last examined mixing speed, where it slightly increases. This is also the case for Mn removal, which enjoys a steep increase at 25 rpm, then, at the next two mixing speeds, a milder increase is observed and thereafter a slower increase with increasing mixing speed. On the other hand, As and Cu removal appears to increase with increasing mixing speeds and achieve >90% removal at the last examined mixing speed. Finally, as was expected, the pH steadily decreases with increasing mixing speeds, and this suggest the higher dissolution of the coagulant at higher mixing speeds. Overall, the 100 rpm mixing speed appears to be optimum, since mixing is an energy intensive process while at the 100 rpm the water has already been decontaminated and the improved removal of As, Cu, and Mn at higher mixing speed does not add further value since their concentration at 100 rpm are already well below the prescribed limits (SANS 241:2015) for drinking water. Similar results were obtained when the commercially available FeCl3coagulant was used to treat the river water (Figure 3b). Again, Mn removal was observed to be higher when using the AMD-synthesized FeCl3for the reasons discussed above. 2.2.3 Effect of contact time The last examined parameter is the effect of contact time. Specifically, six mixing durations, i.e., 1, 2.5, 5, 10, 15 and 30 min, were examined and results are shown in Figure 4. For the AMD-synthesized FeCl3(Figure 4a), increasing mixing durations are beneficial for contaminants removals, since the percentage removals for all examined contaminants / indicators increase with increasing mixing durations. In more detail, it was observed that turbidity, Fe, Al, Cr and Ni removal plateaus at the first examined mixing duration (1 min), whereas colour removal was observed to be 46% at first mixing duration, it slightly increased to 50% plateaus at 5 min mixing duration, and thereafter remained practically stable. For Mn, a high (90%) removal was observed at the first examined mixing duration and thereafter slightly increased with increasing contact time. On the other hand, around 45% of Cu was removed at the first examined mixing duration and this value doubled (81%) at 5 min contact time. Thereafter, its removal only slowly increases with increasing contact time. This is also the case for As, which removal steeply increases in the first two examined mixing durations and then gradually increases until the last examined mixing duration The pH also appears to decrease with increasing contact times, and this can be traced back to FeCl3 increasing dissolution with increasing contact times. As was expected, similar results were obtained for the commercial FeCl3 (Figure 4b). The results are consistent with the ones for coagulant dosage and mixing speed, since the efficiency of the AMD-synthesized FeCl3 in Mn and Fe removal is higher than the ones that the commercial FeCl3 achieves, for the reasons discussed above. Overall, in both cases 5 min appears to optimize treatment efficiency, but not at the expense of energy intensity (higher contact times translate to higher mixing durations). 2.3 Efficacy of the AMD-synthesized coagulant for water and wastewater treatment After the optimum conditions were identified, i.e., 0.2 mL:L dosage and 5 min mixing at 100 rpm, the efficacy of both the AMD-synthesized and the commercial FeCl3for the treatment of raw (river) water as well as of wastewater was examined. 2.3.1 River water The results for the treatment of the real river water, which currently supplies the Cullinan drinking water plant in South Africa, are shown in Table 2. Specifically, the efficacy of the AMD-synthesized coagulant for raw water treatment is on par, and in many instances even better, than the ones obtained when using the commercial FeCl3that is currently employed by the South African drinking water industry. Specifically, for the AMD-synthesized FeCl3the removal efficacies were, from higher to lower score: Al≥ ammonia≥ turbidity≥ Fe≥ Cr≥ Ni≥ COD≥ Mn≥ Cu≥ nitrite≥ nitrate≥ colour ≥ Ca ≥ alkalinity≥ Mg≥ K≥ Na≥ sulfate≥ EC≥ pH with 99.8 ≥ 99.8 ≥ 99.7 ≥ 99.5 ≥ 99.2 ≥ 98.2 ≥ 95.3 ≥ 92.9 ≥ 81.1≥ 67.6≥ 52≥50≥ 48.8≥ 22.4≥ 11.8≥ 10.1≥ 10≥ 9.7 ≥6.7≥ 4.3% removal, respectively. Similar results were obtained for the commercial FeCl3, with the removal efficacies for the same contaminants / parameters being ammonia≥ turbidity ≥ Fe ≥ Cr ≥ Al≥ Ni≥ COD≥ Mn≥ Cu≥ Ca≥ colour≥ nitrate≥ alkalinity≥ nitrite≥ Mg≥ K≥ sulfate≥ Na ≥ pH≥ EC, with 99.8 ≥ 99.6 ≥ 99.4 ≥ 99.2 ≥ 99.1 ≥ 98.2 ≥ 94.4 ≥ 91.4 ≥ 66.9≥ 46.3≥ 39.3≥28≥ 26.6≥ 24.3≥ 11.8≥ 9.1≥ 6.5≥ 5≥ 4.8≥ 3.3% removal, respectively. Therefore, in both cases, river water was treated to a large extent, but more importantly the values for all examined contaminants / indicators were within the South African National Standard for drinking water, i.e., SANS 241:2015 specifications. Overall, the performance of the AMD synthesized coagulant is on par with, and in some instances even better than the commercial Fe(III). Finally, even though river water and surface water in South Africa is typically heavily polluted (Zachary et al., 2018), the identified FeCl3 dosage suggest that the river water is not severely polluted, since, for example, in a case study for canal water treatment in Pakistan the optimum FeCl3dosage was 13 mg / L (Haydar et al., 2010). Table 2: The physicochemical parameters of the raw and the FeCl3treated river water. Units Raw L Synthesized Commercial water imits FeCl3FeCl3Turbidity NTU 265 ≤ 1.0 0.891 0.981 pH - 8.4 ≥5.0 to ≤9.7 8.04 8.0 mS / EC m 30 ≤ 170 28 29 Sulfate mg / L 31 ≤250 28 29 Fe µg / L 600 ≤300 3.1 3.5 Mn µg / L 14 ≤100 1 1,2 Al µg / L 1120 ≤300 2.2 9.8 Cr µg / L 7.8 ≤50 0.06 0.06 Cu µg / L 14.8 ≤2000 2.8 4.9 Ni µg / L 5.1 ≤70 0.09 0.09 ≥250 to ≤ Alkalinity mg / L 192 300 149 141 Zn mg / L 0.02 ≤5.0 0.02 0,02 Colour mg / L 28 ≤15 14 17 Ca mg / L 41 ≤300 21 22 Mg mg / L 17 ≤100 15 15 Ammoni a mg / L 3.9 ≤1.5 0.009 0.009 COD mg / L 213 0.0 10 12 Na mg / L 20 ≤200 18 19 K mg / L 9.9 ≤100 8.9 9 Nitrate mg / L 0.25 ≤11 0.12 0.18 Nitrite mg / L 0.037 ≤0.9 0.012 0.028 2.3.2 Municipal wastewater treatment The efficiency of the AMD-synthesised FeCl3was also tested for wastewater treatment, using the effluent of two municipal wastewater treatment plants, i.e., plant 1 (P1) and plant 2 (P2). The same conditions as the ones for raw water were employed, i.e., 0.2 mL / L dosage, 5 min contact time, and 100 rpm mixing speed. First, the results for plant 1 are given (Table 3), where it can be seen that both the AMD-synthesised and the commercial FeCl3greatly reduced the contaminants load. Table 3: The physicochemical parameters of municipal wastewater from the first treatment plant (P1), before and after its interaction the AMD- synthesized and the commercial FeCl3. (Conditions: 0.2 mL:L dosage at 100 rpm mixing speed, followed by 60 min settling time at ambient temperature and pH.) Parameters Units Limits Raw Synthesized FeCl3Commercial FeCl3 Turbidity NTU <5 80 1.9 1.9 pH - 5.5-9 8.2 7.92 7.91 EC mS / m 0-700 258 251 251 Sulfate mg / L 0-500 39 36 37 Fe µg / L 0-0.1 245 37 39 Mn µg / L 0-0.05 262 20 28 Al µg / L 120 2.2 2.9 Cr µg / L 0.01 32 2.5 2.8 Cu µg / L 0-1 65 19 17 Ni µg / L 0-0.07 105 12 12 Alkalinity mg / L 749 749 749 Zn mg / L 0-0.5 0,04 0,03 0,02 Colour mg / L 210 200 190 Ca mg / L 0-32 210 38 37 Mg mg / L 0.30 140 8,8 8,3 Ammonia mg / L 1 25 1.9 2.1 COD mg / L 250 455 68 69 Na mg / L 0-50 84 81 84 K mg / L 0-50 99 93 95 Nitrate mg / L 15 171 75 150 Nitrite mg / L 15 30 10 10 Specifically, as shown in Table 3, the interaction of the wastewater with the AMD-synthesized FeCl3with the municipal wastewater greatly improved its quality, with the percentage removal efficiencies exhibiting the following pattern, from higher to lower score: 98.2≥ 97.6 ≥ 93.7 ≥ 92.4 ≥ 92.4 ≥ 92.2 ≥ 88.6 ≥ 85.1 ≥ 84.9 ≥ 81.9≥ 70.8≥ 66.7≥ 56.1≥ 25≥ 7.7≥ 6.1≥ 4.8≥ 3.6≥3.4 ≥2.7% for Al≥turbidity≥ Mg ≥ ammonia ≥ Mn ≥ Cr≥ Ni≥ COD≥ Fe≥ Ca≥ Cu≥ nitrite ≥ nitrate≥ Zn≥ sulfate≥ K≥ colour ≥ Na≥ pH≥ EC, respectively. Similar results were obtained for the commercial FeCl3, since the following sequence was obtained: 97.6≥ 97,6≥ 94.1 ≥ 91.6 ≥ 91.3 ≥ 89.3 ≥ 88.6 ≥ 84.8≥ 84.1 ≥ 82.4≥ 73.8≥ 66.7≥50≥ 12.3≥ 9.5≥ 5.1≥ 4≥ 3.5≥2.7 for turbidity≥ Al ≥Mg ≥ ammonia ≥ Cr ≥ Mn≥ Ni≥ COD≥ Fe≥ Ca≥ Cu≥ Zn ≥ nitrate≥ colour≥ sulfate≥ K≥ pH ≥ EC, respectively. As such, the performance of the AMD-synthesized FeCl3is comparable to that of the commercial FeCl3. Similar results were obtained for the effluent of the second treatment plant (P2) (Table 4). Specifically, the interaction of the P2 effluent wastewater with the AMD-synthesized FeCl3yielded the following removal efficiencies, from higher to lower score: 99.5 ≥ 98.2≥ 97.5 ≥ 97.0 ≥ 95.2≥ 67.1 ≥ 61.2 ≥ 55 ≥ 50.0 ≥ 43.0≥ 27.8≥ 21.0≥ 16.7≥ 10.3≥ 6.8≥ 4.3≥ 4.1≥ 2.9% for turbidity≥ Al≥ Mn ≥ COD≥ Cu≥ ammonia ≥ Fe≥ nitrate≥ Cu≥ nitrite≥ colour≥ K≥ Ni≥ Mg ≥ Ca≥ EC≥ pH≥ alkalinity≥ Na, respectively. For the commercial FeCl3the following sequence was recorded: 99.3≥ 96.8 ≥ 96.1 ≥ 91.6≥ 58.6 ≥ 46.0 ≥ 38.9 ≥ 25 ≥ 25≥ 19.5≥ 16.7≥11.0≥ 6.6≥ 5.7≥ 4.2≥ 3.6≥ 2.1≥1.0% for turbidity≥ COD ≥ Al≥ Mn ≥ Cu ≥ Fe≥ nitrate≥ nitrite≥ colour≥ ammonia≥ K≥ Ni ≥ alkalinity≥ EC≥ Mg≥ pH≥ Ca ≥ Na, respectively. Therefore, the recorded removal efficiencies for the P2 effluent are similar for both the AMD- synthesized and commercial FeCl3 and are also comparable with the ones recorded for the P1 effluent, even though their initial characteristics were not quite similar. Therefore, results suggest that the AMD-synthesized ferric salt can be effectively used for the treatment of raw water and wastewater, while the optimum treatment conditions will depend on the initial characteristics of the treated water matrix. Overall, the beneficiation (Fe(III) recovery) of a wastewater matrix (AMD) and its subsequent use to effectively treat other water and wastewater matrices can protect the receiving environment and also can safeguard human health, through safe and affordable clean water which is in line with the United Nations (UN) sustainable development goals (SDGs). Table 4: The physicochemical parameters of municipal wastewater from the second treatment plant (P2), before and after its interaction the AMD- synthesized and the commercial FeCl3. (Conditions: 0.2 mL:L dosage at 100 rpm mixing speed, followed by 60 min settling time at ambient temperature and pH.) Synthesized Parameters Units Raw FeCl Commercial FeCl33 Turbidity NTU 229 1,2 1,5 pH - 8,1 7,75 7,81 EC mS / m 88 82 83 Sulfate mg / L 70 70 70 Fe µg / L 276 107 149 Mn µg / L 44 1,1 1,7 Al µg / L 62 1,1 5,4 Cr µg / L 0,06 0,06 0,06 Cu µg / L 29 1,4 12 Ni µg / L 10 7,9 8,9 Alkalinity mg / L 320 307 299 Zn mg / L 0,02 0,02 0,02 Colour mg / L 100 57 75 Ca mg / L 39 35 38 Mg mg / L 24 20 23 Ammonia mg / L 39,5 13 31,8 COD mg / L 693 21 22 Na mg / L 103 100 102 K mg / L 18 13 15 Nitrate mg / L 1,8 0,81 1,1 Nitrite mg / L 0,28 0,14 0,21 3 Conclusions The present invention provides for the recover of Fe(III) from acid mine drainage (AMD), a highly acidic and bio-recalcitrant wastewater matrix, and ferric salt (ferric chloride, FeCl3) production. The AMD-synthesized FeCl3 was used for the treatment (coagulation) of real raw water and wastewater treatment. Specifically, river water that feeds a water treatment plant in South Africa was collected and effectively treated when using 0.2 mL / L (v / v ratio) FeCl3 dosage, for a contact time of 5 min and mixing speed 100 rpm. Under those conditions the percentage removal efficacies for contaminants / indicators was the following: 99.8 ≥ 99.8 ≥ 99.7 ≥ 99.5 ≥ 99.2 ≥ 98.2 ≥ 95.3 ≥ 92.9 ≥ 81.1≥ 67.6≥ 52≥50≥ 48.8≥ 22.4≥ 11.8≥ 10.1≥ 10≥ 9.7 ≥6.7≥ 4.3% for Al≥ ammonia≥ turbidity≥ Fe≥ Cr≥ Ni≥ COD≥ Mn≥ Cu≥ nitrite≥ nitrate≥ colour ≥ Ca ≥ alkalinity≥ Mg≥ K≥ Na≥ sulfate≥ EC≥ pH respectively. Similar results were obtained when the same raw water was treated with commercially available FeCl3, which is already used by the water and wastewater industry in South Africa. Specifically, for the same river water matrix the commercially available FeCl3 achieved the following percentage removal efficiencies: 99.8 ≥ 99.6 ≥ 99.4 ≥ 99.2 ≥ 99.1 ≥ 98.2 ≥ 94.4 ≥ 91.4 ≥ 66.9≥ 46.3≥ 39.3≥28≥ 26.6≥ 24.3≥ 11.8≥ 9.1≥ 6.5≥ 5≥ 4.8≥ 3.3 for ammonia≥ turbidity ≥ Fe ≥ Cr ≥ Al≥ Ni≥ COD≥ Mn≥ Cu≥ Ca≥ colour≥ nitrate≥ alkalinity≥ nitrite≥ Mg≥ K≥ sulfate≥ Na ≥ pH≥ EC, respectively. The results also highlighted that the AMD-synthesized FeCl3did not contain toxic heavy metals in its matrix, while the treated river water itself was within South African specifications for drinking water quality (SANS 241:2015). This implies that the AMD-synthesized FeCl3 is chemically stable and does not pose any toxicological and hazardous effects. Not only this, but the efficiency of the AMD-synthesized FeCl3 was found also to be on par the one of the commercially available FeCl3 for municipal wastewater treatment. Therefore, results demonstrate the feasibility of replacing commercial Fe(III)-based coagulants with the ones produced from Fe(III) that has been recovered from AMD. This can create opportunities for sustainable water and wastewater treatment and the introduction of circular economy through waste beneficiation and reuse. All ranges disclosed herein include both endpoints and all numbers between the endpoints.

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Claims

CLAIMS 1. A process for preparing ferric chloride for a water treatment process for producing potable water comprising: (a) adding magnesium oxide to acid mine drainage (AMD) to produce a Fe(III) precipitate and a supernatant, (b) separating the Fe(III) precipitate from the supernatant, (c) optionally, drying the Fe(III) precipitate, (d) reacting hydrochloric acid with Fe(III) precipitate to produce ferric chloride rich solution, (e) using the ferric chloride rich solution in a water treatment process for producing potable water.

2. The process as claimed in claim 1, wherein the pH after step (a) is about 2.5 to about 4.5, or 3.

5.

3. The process as claimed in claim 1 or 2, wherein the hydrochloric acid is industrial grade hydrochloric acid.

4. The process as claimed in any one of claims 1 to 3, wherein the hydrochloric acid is present at a concentration of about 30%.

5. The process as claimed in any one of claims 1 to 4, wherein step (a) occurs by stirring in a mixer at a speed of between 300 rpm and 700 rpm, between 400 rpm and 600 rpm, or 500 rpm for between 20 to 50 minutes, between 25 to 40 minutes, or about 30 minutes.

6. The process as claimed any one of claims 1 to 5, wherein the resultant mixture of step (a) is left to equilibrate to allow the Fe(III) precipitate to separate from the supernatant in the mixture for between 15 minutes to 1 hour, 20 minutes to 50 minutes, or about 30 minutes.

7. The process as claimed in any one of claims 1 to 6, wherein step (b) occurs using a gravity filter, vacuum pump filter or gravity settling to separate Fe(III) precipitate from the supernatant.

8. The process as claimed in any one of claims 1 to 7, wherein step (c) is present, the Fe(III) precipitate is oven dried.

9. The process as claimed in claim 8, wherein the Fe(III) precipitate is oven dried at 90 - 900oC, 95oC - 500oC or 105oC for around 1 - 24 hours or 24 hrs.

10. The process as claimed in any one of claims 1 to 9, wherein step (d) occurs in a chlorination process to produce ferric chloride rich solution.

11. The process as claimed in any one of claims 1 to 10, wherein in step (e) the ratio of Fe(III) to water to be treated is in the ratio of 0.1 to 1 mL:L or 0.1, 0.2.0.4, 0.6, 0.8 or 1 mL:L.

12. The process as claimed in any one of claims 1 to 11, wherein the mixing step at step (e) is mixed at a speed of 25, 50, 100, 150, 200 or 250 rpm.

13. The process as claimed in claim 12, wherein mixing time for contact between the ferric chloride and water to be treated is 1, 2.5, 5, 10, 15 or 30 mins.

14. The process as claimed in any one of claims 1 to 13, wherein the potable water may be left to settle for about between 30 to 120 minutes, between 45 minutes to 90 minutes or 60 minutes.

15. The process as claimed in any one of claims 1 to 14, wherein the potable water produced at step (e) have a pH in the range of between about 6 to 8, 7.7 to about 8.1 or 7 and 7.

9.

16. The process as claimed in any one of claims 1 to 15, wherein one or more of the following contaminants may be removed from the water to be treated in step (e) with ±10%: Al of about 99.8%, ammonia of about 99.8%, turbidity of about 99.7%, Fe of about 99.5%, Cr of about 99.2%, Ni of about 98.2%, COD of about 95.3%, Mn of about 92.9%, Cu of about 81.1%, Nitrite of about 67.6%, Nitrate of about 52%, colour of about 50%,Ca of about 48.8%, alkalinity of about 22.4%, Mg of about 11.8%, K of about 10.1%, Na of about 10%, sulfate of about 9.7%, EC of about 6.7% and pH of about 4.3%.

17. The process as claimed in any one of claims 1 to 16, wherein the AMD is prefiltered before adding magnesium oxide.

18. A method for producing potable water comprising using a ferric chloride rich solution in a water treatment process for producing potable water, wherein the ferric chloride rich solution is prepared using the following process: (a) adding magnesium oxide to acid mine drainage (AMD) to produce a Fe(III) precipitate and a supernatant, (b) separating the Fe(III) precipitate from the supernatant, (c) optionally, drying the Fe(III) precipitate, (d) reacting hydrochloric acid with Fe(III) precipitate to produce ferric chloride rich solution.

19. The method as claimed in claim 18, wherein the pH after step (a) is about 2.5 to about 4.5, or 3.

5.

20. The method as claimed in claim 18 or 19, wherein the hydrochloric acid is industrial grade hydrochloric acid.

21. The method as claimed in any one of claims 18 to 20, wherein the hydrochloric acid is present at a concentration of about 30%.

22. The method as claimed in any one of claims 18 to 21, wherein step (a) occurs by stirring in a mixer at a speed of between 300 rpm and 700 rpm, between 400 rpm and 600 rpm, or 500 rpm for between 20 to 50 minutes, between 25 to 40 minutes, or about 30 minutes.

23. The method as claimed any one of claims 18 to 22, wherein the resultant mixture of step (a) is left to equilibrate to allow the Fe(III) precipitate to separate from the supernatant in the mixture for between 15 minutes to 1 hour, 20 minutes to 50 minutes, or about 30 minutes.

24. The method as claimed in any one of claims 18 to 23, wherein step (b) occurs using a gravity filter, vacuum pump filter or gravity settling to separate Fe(III) precipitate from the supernatant.

25. The method as claimed in any one of claims 18 to 24, wherein step (c) is present, the Fe(III) precipitate is oven dried.

26. The method as claimed in claim 25, wherein the Fe(III) precipitate is oven dried at 90 - 900oC, 95oC - 500oC or 105oC for around 1 - 24 hours or 24 hrs.

27. The method as claimed in any one of claims 18 to 26, wherein step (d) occurs in a chlorination process to produce ferric chloride rich solution.

28. The method as claimed in any one of claims 18 to 27, wherein the ratio of Fe(III) to water to be treated is in the ratio of 0.1 to 1 mL:L or 0.1, 0.

2. 0.4, 0.6, 0.8 or 1 mL:L.

29. The method as claimed in any one of claims 18 to 28, wherein the ferric chloride rich solution is mixed with water to be treated at a speed of 25, 50, 100, 150, 200 or 250 rpm.

30. The method as claimed in claim 29, wherein mixing time for contact between the ferric chloride and water to be treated is 1, 2.5, 5, 10, 15 or 30 mins, preferably 1 min, and most preferably 5 mins.

31. The method as claimed in any one of claims 18 to 30, wherein the potable water may be left to settle for about between 30 to 120 minutes, between 45 minutes to 90 minutes or 60 minutes.

32. The method as claimed in any one of claims 18 to 31, wherein the potable water produced has a pH in the range of between about 6 to 8, 7.7 to about 8.1 or 7 and 7.9.

33. The method as claimed in any one of claims 18 to 32, wherein one or more of the following contaminants may be removed from the water to be treated with ±10%: Al of about 99.8%, ammonia of about 99.8%, turbidity of about 99.7%, Fe of about 99.5%, Cr of about 99.2%, Ni of about 98.2%, COD of about 95.3%, Mn of about 92.9%, Cu of about 81.1%, Nitrite of about 67.6%, Nitrate of about 52%, colour of about 50%, Ca of about 48.8%, alkalinity of about 22.4%, Mg of about 11.8%, K of about 10.1%, Na of about 10%, sulfate of about 9.7%, EC of about 6.7% and pH of about 4.3%.

34. The method as claimed in any one of claims 18 to 33, wherein the AMD is prefiltered before adding magnesium oxide.

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