Circular Process for Phosphoric Acid Plant Wastewater Facilitated by Selective Electrodialysis

Abstract

Phosphoric acid production generates large volumes of industrial wastewater that cannot be treated efficiently by existing processes because of its low pH and high precipitation potential. At present, the wastewater is generally stored in evaporation ponds that are prone to breaches, leakage, and flooding.We developed an alternative three-step process for the treatment of phosphoric acid wastewater including selective electrodialysis, reverse osmosis, and neutralization. Testing the process with synthetic wastewater yielded promising results. An exceptional Na/Ca selectivity (up to 18.3 was observed in low-pH electrodialysis, enabling the separation of concentrated H2SO4 without gypsum scaling. Sulfate removal from the electrodialysis diluate prevented scaling in the subsequent highrecovery (>90%) reverse osmosis step, generating high-quality water. A final reaction between the reverse osmosis concentrate and natural phosphate rock enabled P recovery and neutralization of remaining acidity. The electric-power requirement of the process was estimated to be 4.4 kWh per m 3 of wastewater, from which 0.78 m 3 of clean water, ~3 kg H2SO4, and ~2.5 kg P were recovered. Overall, lab-scale results indicate that this process would be a sustainable and techno-economically viable solution for the treatment of hazardous wastewater byproducts of the phosphoric acid industry.

Scaling-Enhanced Scaling during Electrodialysis Desalination

“…Electrodialysis (ED), an electrically driven ion exchange membrane separation process, has been used for desalinating various types of water, such as seawater and brine, − brackish water, − and wastewater, and separating charged species such as metal ions from liquid streams . However, scaling due to the precipitation of inorganic minerals in the ED stack is one of the critical issues reducing the ED separation performance and hindering its wide applications. − Previous studies found that the scaling on the membrane during ED could lead to the increase in membrane potential difference and overall stack resistance and the decrease in membrane conductivity and ion exchange capacity, , which eventually leads to the decrease in desalination efficiency (DE) and the increase in energy consumption during ED desalination.…”

Teaching Acid–Base Fundamentals and Introducing pH Using Butterfly Pea Flower Tea

“…Young students are often more attentive to visually stimulating reactions in chemistry, , and the opportunity to mix chemicals with their own hands contributes to future chemistry identity on career intention . Acid–base chemistry is a natural phenomenon present in everyday life that is also important in research settings, such as wastewater treatment, , fertilizers, − catalysis, − drug development and delivery. − Additionally, pH indicators provide a direct visual portrayal of the concepts behind acids and bases. Thus, there is a unique opportunity to present acid–base chemistry in an exciting manner to help foster curiosity and drive young students to explore fundamental chemistry.…”

How Chemical Nature of Fixed Groups of Anion-Exchange Membranes Affects the Performance of Electrodialysis of Phosphate-Containing Solutions?

“…The development of low-reagent membrane processes for recovery phosphates from various streams and returning them to production can solve this problem [ 34 , 35 ]. Moreover, electrodialysis has already established itself as a promising method for the extraction and simultaneous concentration of phosphates at the final stage of such circulation schemes [ 36 , 37 , 38 , 39 , 40 ]. Secondly, researchers who are engaged in applied aspects of the development of such electrodialysis processes report low current efficiency [ 36 , 41 ] and relatively high energy consumption [ 42 , 43 ], as well as lower limiting concentrations of phosphates [ 44 , 45 ] which are achieved at electrodialysis processing of phosphate-containing solutions compared to other substances, such as NaCl.…”

“…Moreover, electrodialysis has already established itself as a promising method for the extraction and simultaneous concentration of phosphates at the final stage of such circulation schemes [ 36 , 37 , 38 , 39 , 40 ]. Secondly, researchers who are engaged in applied aspects of the development of such electrodialysis processes report low current efficiency [ 36 , 41 ] and relatively high energy consumption [ 42 , 43 ], as well as lower limiting concentrations of phosphates [ 44 , 45 ] which are achieved at electrodialysis processing of phosphate-containing solutions compared to other substances, such as NaCl. For example, the recovery of chlorides and phosphates is 90% and 40%, respectively, if sweet whey demineralization using ED reaches 70% [ 46 ].…”