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Potential for potassium recovery as K-struvite Bennett, Aline Miriam
Abstract
Crystallization of NH₄-struvite (MgNH₄PO4:6H₂O) pellets has proven to be a successful method of recovering nitrogen and phosphorus from wastewaters. Thus far, little work has been done on potassium recovery since it is not considered a water pollutant, nor do we face potassium shortages. However, potassium is an essential plant macronutrient and we are seeing worldwide imbalances in nutrient and fertilizer use, as well as a need for a slow release potassium fertilizer. Development of a full complement NPK fertilizer with NH₄-struvite and K-struvite components may have great potential. Given this, research into potassium recovery through crystallization of K-struvite (MgKPO₄: 6H₂O) is relevant and complements previous work done with NH₄-struvite. The goals of this research were to develop fundamental understanding of K-struvite formation as the first step to recovering potassium, and eventually produce a full complement NPK slow-release fertilizer from wastewaters. This required the determination of new solubility product values for K-struvite at different temperatures, followed by bench-scale experiments to assess K-struvite synthesis under various solution conditions. A model to simulate each batch experiment and to predict optimal supersaturation conditions for K-struvite precipitation was developed using PHREEQC, aqueous equilibrium modelling software. Finally, initial experiments in the UBC fluidized bed reactor (UBC-FBR) were undertaken to assess the pelletization potential of K-struvite. New solubility product values for K-struvite indicate that it is less soluble than previously reported, and the values determined at 10, 25 and 35°C fit the Van’t Hoff model. Optimal Mg:K:P molar ratio for synthesis of pure K-struvite was found to be approximately 3:50:1 in a wastewater matrix with pH 8, P-PO₄ concentration of 8 mM and a Mg:P ratio of 3:1. These concentrations were used in the UBC-FBR to assess the pelletization potential of K-struvite. These initial reactor runs were inconclusive due to an inability to stabilize the reactor without seeding. It would be recommended to seed the reactor during start-up in order to be able to compare process performance with the NH₄-struvite crystallization process in the UBC-FBR. This study showed that formation of pure K-struvite is possible given the right supersaturation conditions in solution, requiring high potassium concentrations.
Item Metadata
Title |
Potential for potassium recovery as K-struvite
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2015
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Description |
Crystallization of NH₄-struvite (MgNH₄PO4:6H₂O) pellets has proven to be a successful method of recovering nitrogen and phosphorus from wastewaters. Thus far, little work has been done on potassium recovery since it is not considered a water pollutant, nor do we face potassium shortages. However, potassium is an essential plant macronutrient and we are seeing worldwide imbalances in nutrient and fertilizer use, as well as a need for a slow release potassium fertilizer. Development of a full complement NPK fertilizer with NH₄-struvite and K-struvite components may have great potential. Given this, research into potassium recovery through crystallization of K-struvite (MgKPO₄: 6H₂O) is relevant and complements previous work done with NH₄-struvite.
The goals of this research were to develop fundamental understanding of K-struvite formation as the first step to recovering potassium, and eventually produce a full complement NPK slow-release fertilizer from wastewaters. This required the determination of new solubility product values for K-struvite at different temperatures, followed by bench-scale experiments to assess K-struvite synthesis under various solution conditions. A model to simulate each batch experiment and to predict optimal supersaturation conditions for K-struvite precipitation was developed using PHREEQC, aqueous equilibrium modelling software. Finally, initial experiments in the UBC fluidized bed reactor (UBC-FBR) were undertaken to assess the pelletization potential of K-struvite.
New solubility product values for K-struvite indicate that it is less soluble than previously reported, and the values determined at 10, 25 and 35°C fit the Van’t Hoff model. Optimal Mg:K:P molar ratio for synthesis of pure K-struvite was found to be approximately 3:50:1 in a wastewater matrix with pH 8, P-PO₄ concentration of 8 mM and a Mg:P ratio of 3:1. These concentrations were used in the UBC-FBR to assess the pelletization potential of K-struvite. These initial reactor runs were inconclusive due to an inability to stabilize the reactor without seeding. It would be recommended to seed the reactor during start-up in order to be able to compare process performance with the NH₄-struvite crystallization process in the UBC-FBR.
This study showed that formation of pure K-struvite is possible given the right supersaturation conditions in solution, requiring high potassium concentrations.
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Genre | |
Type | |
Language |
eng
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Date Available |
2016-07-31
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-ShareAlike 2.5 Canada
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DOI |
10.14288/1.0166487
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2015-09
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Attribution-NonCommercial-ShareAlike 2.5 Canada