The ROC Process
ROC Water Technologies
ROC Water Technologies focus on the treatment of saline waters with the aim to recover drinking water and saleable products using a four-stage process (neutralization, desalination with reverse osmosis, brine treatment with freeze crystallization and product recovery with thermal treatment. Valuable products to recover include: (i) pigment from ferric hydroxide in the neutralization stage, (ii) drinking water from the desalination stage (iii) sodium sulphate from the freeze crystallization stage and (iv) sodium carbonate from sodium sulphate in the thermal stage. This technology aims to: (i) achieve zero waste through product recovery and (ii) income to exceeds the cost.
Methods We Use
Limestone Neutralization
ROC Water Technologies focus on the treatment of saline waters with the aim to recover drinking water and saleable products using a four-stage process (neutralization, desalination with reverse osmosis, brine treatment with freeze crystallization and product recovery with thermal treatment.
Precipitated calcium carbonate is a by-product from the paper industry and has been used in Australia, Botswana an several places in South Africa for neutralization of acidic effluents from the mining and heavy mineral industries. As it contains 15% moisture, a limestone handling and dosing system has been developed to slurry it before dosing for neutralization. The cost of precipitated calcium carbonate amounts to R1 050/t compared to the R3 950/t for slaked lime (Ca(OH)2).
In-situ treatment can also be used and offers the following benefits:
- Partial desalination due to gypsum crystallization to its saturation level (typically 3 500 mg/l SO4)
- Waste sludge, that is settled out, is already at the disposal site and will not require further handling.
- Treatment can be completed in a short period when security is provided. Equipment can then be removed and returned after the dam has been filled again after 200 days.
- Low capital cost. The capital cost is less than R1 million / (ML/d), which is low compared to the R9 million / (ML/d) in the case of continuous treatment.
- Immediate treatment is possible.
Freeze Crystallization
ROC Water Technologies focus on the treatment of saline waters with the aim to recover drinking water and saleable products using a four-stage process (neutralization, desalination with reverse osmosis, brine treatment with freeze crystallization and product recovery with thermal treatment.
Highly saline water can be treated with freeze crystallization to remove clean water via ice formation. The remaining brine becomes more concentrated with salts, until the salts start to crystallize. Salts can be removed selectively according to its solubilities. In the case of water rich in Na2SO4 and NaCl, the Na2SO4 will crystallize first due to its lower solubility of 45 g/L. NaCl will crystallize last because of its high solubility of 350 g/L.
Freeze crystallization approach is cheaper and does not require a lot of equipment to implement, i.e. it involves unit operations like heat exchangers, crystallizers, separators and melters, which ultimately forms an integrated wastewater purification system. Its benefits include low energy requirements when compared to other methods such as evaporation systems. Additionally, it is a chemical-free separation method and offers simultaneous crystallization and recovery of water (ice) and salt.
Cost Benefit of Freeze Crystallization versus Disposal
| Cost Item | Unit | Amount |
|---|---|---|
Capital cost for 0.1 m3/h plant | ZAR | 1 500 000 |
Capital redemption cost (5%/year; 120 months) | ZAR/m3 | 225 |
| Electricity (100 kWh/t ice, ZAR 2.0/kWh) | ZAR/m3 | 200 |
| Labour | ZAR/m3 | 150 |
| Maintenance | ZAR/m3 | 25 |
| Chemicals | ZAR/m3 | 5 |
Total cost of Freeze Crystallization | ZAR/m3 | 605 |
Disposal cost at toxic waste disposal sites Value of products not included | ZAR/m3 | 2500 |
Thermal Treatment
ROC Water Technologies focus on the treatment of saline waters with the aim to recover drinking water and saleable products using a four-stage process (neutralization, desalination with reverse osmosis, brine treatment with freeze crystallization and product recovery with thermal treatment.
Pigment can be recovered from ferric hydroxide, produced during the neutralization of iron-rich acid mine water. At 200 °C the yellow goethite is produced and at 800 °C the red hematite is produced.
Gypsum can be processed to nano calcium carbonate and sulfur by reacting it with coal at 1000 °C. Similarly, sodium carbonate can be recovered from sodium sulphate.
ROC process
T Mtombeni and J P Maree (2014) Treatment of water – ROC process, ROC Water Technologies, RSA (No 2015/04639), Germany (No 3452414), France (No 3452414), Australia (No 2016405754 – Pending), USA No 16/099,009)
Magnetite/Pigment process
J P Maree (2016) Recovery of magnetite from acid mine water, South African RSA Patent 2017/03047; Provisional Patent Application, 2016/00875; Owner: Phillert Trust who provided a license to ROC Water Technologies
Pipe Freeze Crystallization
J P Maree (2018) Pipe Freeze Crystallization, ROC Water Technologies, Provisional Application No: 2018/04084, RSA No: 2019/03795, Australia No: 201204324 (pending), Canada No: 3,092,764 (pending), USA No: 17,027,873.
Sodium carbonate production
van Vuuren D S, Maree J P (2020) Production of sodium carbonate from sodium sulphate, Provisional Patent Appl. No 2020/07178, University of Pretoria and University of Limpopo, Filing date: 18 November 2020; PCT patent application (2022).
Nano calcium carbonate
Maree J P, van Vuuren D S, (2021) Production of nano calcium carbonate, Provisional Patent Appl. 2021/07244, University of Limpopo and ROC Water Technologies, Filing date: 29 Sept 2021; RSA patent (2022)
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