ZLD Recovery Options

Desalination of high saline waters is becoming more and more common for supporting a growing water demand around the world. Desalination though doesn’t come cheap. There are multiple problems associated with desalination, which are mainly,

1. CAPEX and OPEX
2. Brine management and disposal

Brine disposal can be a significant portion of total project costs, depending on,

1. Volume
2. Type of discharge

In order to deal with brine management, there have been increasing efforts worldwide to reduce brine volumes with zero liquid discharge (ZLD) technologies.

One option to decrease the ZLD-relative costs is be recovering the valuable contaminants in the desalination brine streams. This way the recovered materials could be sold and thus raise the profits of a desalination plant. Alternatively the recovered materials could be used within the industrial facility using the desalination process and so reduce the operation cost.

The feasibility of the material recovery process from brine depends from the technical limitations of the available technologies and their energy and cost considerations, but also from the market fluctuations for the materials that are recovered.

A rough approach for the feasibility of a mineral recovery project is the following algorithm, where the potentially profitable stream contaminants need to fulfill the inequality,

P * C * Q_c - OM > 0

Where,

P = market price of the material

C = concentration of the element in the brine

Q_c = flow rate of the brine

OM = the operational and maintenance (O&M) costs

In the following table we present the main opportunities for material recovery from desalination brine,

Element	Main commodities	Market opportunities
Bromine	Elemental bromine (Br2) Organobromide fertilizers  Flame retardants  Gasoline additives	- ↑ demand expected in Asia and South America - Boron reserves will satisfy global demand for the foreseeable future
Calcium	Calcium carbonate, Lime (CaO) Calcium sulfate  Calcium chloride	- ↑ demand expected in USA - ↑ production of gypsum from coal-fired power plant scrubbers  expected   - possible applications for low quality commodities: CaCl2 in dust suppression; and CaCl2 or CaSO4 use in sodic soil remediation - CaCO3 pellets produced at BWRO facility and sold
Cesium	Cesium metal	- ↓ market as drilling fluid, drill pipe unsticking, and treatment of some tumors
Chlorine and Sodium Hydroxide	Chlorine gas (Cl2)  Hypochorous acid Solid NaOH Concentrated liquid NaOH	- ↑ demand for sodium hydroxide for the last 5 years - ↓ Chlorine demand due to the global economic recession
Magnesium	Magnesium metal  Magnesia Mg(SO4), Mg(OH)2, MgCl2, MgO-Synthetic	- production of magnesium metal from seawater is not competitive with current methods of production - ↑ demand expected for caustic calcined magnesia and magnesium hydrioxide in the near future - U.S. currently imports the majority of consumed magnesia
Nitrogen	Ammonia, Urea Ammonium nitrate Ammonium phosphates Ammonium sulfate Nitric acid	- ↑ demand expected worldwide for nitrogen consumption for fertilizers - because of stable natural gas prices, nitrogen fixing production is expanding
Potassium	Potash (K2O) in the form of either potassium chloride, potassium sulfate, or potassium magnesium sulfate	- ↑ by 4% annually worldwide for potash consumption due to population growth and increased fertilizer demand - Potassium as a fertilizer has no substitutes.
Rubidium	Rubidium metal  Rubidium carbonate Rubidium chloride Rubidium hydroxide Rubidium silver iodide	-  probable ↑interest in the use of rubidium for quantum computing, in atomic clocks and superconductors, and for biomedical uses. - little demand
Sodium	Salt Sodium Hydroxide Sodium sulfate	- Sodium compounds are consumed in ↑ quantities by a variety of end users and industries
Strontium	Strontium metal Strontium carbonate Strontium nitrate Strontium oxide (strontia)  Strontium hydroxide Strontium peroxide Celestite (strontium sulfate)	- ↓ strontium demand since 1997 - Strontium consumption is expected to ↑ in the near future, in traditional applications (e.g., ceramics, glasses and magnets), and advanced applications (e.g., pharmaceuticals)
Lithium	Lithium carbonate Lithium hydroxide Lithium chloride	- ↑ demand expected due to ↑ lithium-ion battery production.
Uranium	Triuranium octoxide	- ↑ worldwide demand projected to reach 110 kton-U/yr by 2030. - Uranium extracted from seawater costs could be between 220-280$/ kg-U with the prices reported to fall between 689–2850/ kg-U