Introduction

Natural brines and other mineral sources contain multiple inorganic salt components such as lithium (Gao et al., 2012), iron and base-metal-rich sulfide, magnesium, and chloride (Nishri et al., 1988). However, recovery of these inorganic salts from aqueous saline systems is a challenging task due to their high solubility (Foo et al., 2022). Technologies for recovering these salts from the concentrated brines are limited and in most cases, the concentrated brine solutions are ejected into the sea (Vallès et al., 2023). Precipitation and crystallization-based techniques have been exploited commercially for inorganic salt recovery from natural brines and mineral reserves. Recent studies in the crystallization space indicate antisolvent crystallization as a promising technique that offers several advantages over traditional methods (Moldoveanu and Demopoulos, 2015). Some of the advantages of antisolvent crystallization include, low energy requirement, ambient operating temperature, and the capability to recover and reuse solvents rather than discharging back to the ecosystem, thereby leading to reduced costs and environmental impacts (Raj R and kurup, 2016). In this study, we analyzed the techno-economics of an antisolvent crystallization process for the recovery of sodium chloride and sodium sulphate from bittern.

Methodology

During salt production via desalination process, a major byproduct is the concentrated aqueous solution of multiple salts, also known as bittern. This bittern is rich is sodium sulphate as well as leftover sodium chloride (Battaglia et al., 2023).

To understand the recovery of these salts selectively from bittern we first conducted laboratory experiments to determine the process conditions for optimal crystallization yield. We used several candidate antisolvents such as ethanol, methanol, acetone, acetonitrile, ethylene glycol and dimethyl sulfoxide and based on the dissolution test runs, we evaluated and chose ethanol for the study. Ethanol is chosen as the solvent due to its potential for high crystallization yields and its relatively low environmental impact as a greener organic solvent.

We further conducted a detailed mass balance, and energy consumption estimates for the process. We estimated the total product cost which encapsulated the raw material cost, utility cost, overhead cost (other cost), labor cost, equipment cost and cost of consumables. The cost of the equipment and other consumables were taken from SuperPro Designer databanks using the base cost analysis for the year 2023. The minimum weighted selling price for the recovered salts (NaCl and Na₂SO₄) required to achieve profit is estimated and thus the break-even profitability metric was used in the analysis. The process schematic is represented in Figure 1.

Results

The economics and process sustainability of the antisolvent crystallization process for selective inorganic salt recovery from concentrated aqueous saline is presented in this work. The economic viability of the inorganic salt (NaCl and Na₂SO₄) recovery process with a capacity of 8 tons/day is evaluated with an annualized capital cost evaluated using a capital recovery factor of 0.11, assuming a plant life of 25 years. The evaluated cost distribution for the process shown that the total cost for operation is highly influenced by the utility cost and the cost of the solvent. The total production cost is analyzed for the process with solvent recovery and also with no solvent recovery.

The raw material cost for the recovery process is calculated from the equation

Raw material (RM) cost = cost of RM – cost of RM (recovery) = C_I*M_J - C_I*rM_J

Overall, this study contributes to the development and the adoption of circular economy principles, which is an economic model that aims to reduce waste and promote the efficient use of resources. The circular economy model is based on the principles of reducing, reusing, and recycling materials to create a closed loop system. Antisolvent crystallization with solvent recovery contributes to circular economy by enabling the reuse of solvents, reducing waste generation and conserving resources. Additionally, the recovered solvent is reused in subsequent processes, reducing the need for new materials and promoting a closed loop system.

REFERENCES

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