As Future Generations Will Need to Live on Our Trash: Recovery of Phosphorous and Fluorine from Phosphogypsum.
The paper to which I'll briefly refer in this post is this one: Investigation on the Mechanism of Efficient Removal of Phosphorus and Fluorine Impurities from Phosphogypsum by an In Situ Recrystallization Purification Method Daping Chen, Jinbao Song, Jupei Xia, Binbin He, Qiongbo Zhou, Yidong Hou, Yunxiang Nie, and Yi Mei Industrial & Engineering Chemistry Research 2024 63 (51), 22369-22379.
The world food supply depends on two major contributors to fertilizer, fixed nitrogen, which in theory and in (rather dirty) practice is available via the Haber-Bosch process, now overwhelmingly produced using hydrogen prepared from the steam reforming of dangerous fossil fuels, and phosphorous, which is mined, and thus subject to depletion. The paper refers to the waste products of phosphorous mining, which still contains some industrially inaccessible phosphorous, as well as the industrially important element fluorine.
My interest in the paper was driven by scale, the quantity of waste phosphogypsum, which is reportedly 6 billion tons.
From the introductory text:
Phosphogypsum, whose main component is calcium sulfate dihydrate (CaSO4·2H2O), is an industrial solid waste generated during the production process of wet process phosphoric acid. (1,2) Up to 4–6 tons of phosphogypsum will be produced when 1 ton of phosphoric acid product is obtained. (3,4) The global inventory of phosphogypsum has exceeded 6 billion tons, and it is expanding at a rate of 150 million tons annually. However, due to its high proportion of harmful impurities, the comprehensive utilization rate of phosphogypsum is only about 15%, and most countries still rely mainly on inventory. (5) According to the statistics from the China Phosphate and Compound Fertilizer Industry Association, the production of phosphogypsum in China exceeded 80 million tons in 2021, and the total storage capacity in 2022 has reached 700 million tons, ranking first in the world. (6) The long-term accumulation of a large amount of phosphogypsum has occupied valuable land resources. In addition, the harmful impurities such as phosphorus, fluorine, and metal ions contained in phosphogypsum, once immersed in groundwater, rivers, and lakes, can cause severe water contamination and seriously threaten human life safety. (7,8) At present, phosphogypsum is mainly used to prepare cement retarders, building gypsum powder, soil amendments, roadbed materials, etc., but its comprehensive utilization rate is less than 50%. (9−11) The phosphorus and fluorine impurities from phosphogypsum can affect the performance and quality of subsequent products, seriously restricting their large-scale application. (12) Therefore, to effectively solve the storage and utilization problems of phosphogypsum, it is crucial to eliminate phosphorus and fluorine impurities...
The authors propose a relatively mild procedure for recovering the valuable elements from this waste product.
I will not have time to go into many of the details, but the paper in its conclusions gives the process conditions which involve rather mild conditions accessible from process intensification using heat networks as well as mechanical tools:
In this article, an effective method for removing phosphorus and fluorine impurities from phosphogypsum through in situ recrystallization and washing was investigated. The experimental results show that the optimal impurity purification conditions are as follows: stirring rate of 100 r/min, liquid–solid mass ratio of 3:1, recrystallization time of 40 min, recrystallization temperature of 50 °C, washing temperature of 70 °C, and 3 washing cycles. The removal efficiencies of phosphorus and fluorine are 86.4% and 95.71%, respectively, exhibiting a better purification effect. In addition, the purification mechanism for phosphogypsum is elucidated. During the recrystallization and washing process of FPG, CaSO4·0.5H2O dissolves and then transforms into larger rhombic CaSO4·2H2O particles. In the meantime, the impurities, such as water-soluble phosphorus (H3PO4, H2PO4–, HPO42–, and Ca(H2PO4)2), eutectic phosphorus (CaHPO4·2H2O), and water-soluble fluorine (F–, Na2SiF6, and K2SiF6), carried in FPG are transferred from the solid phase to the liquid phase, thereby achieving purification of phosphogypsum. It is worth noting that some of the eutectic phosphorus entrained in phosphogypsum also dissolves in the liquid phase. The purified phosphogypsum can meet the requirements for producing cement retarders and gypsum blocks.
The paper contains a photograph of a pilot plant attached to an industrial facility in China. It is capable of processing 1.5 million tons per year.
We have screwed future generations royally, and the world is sinking into a vast political garbage heap of proto and actual fascism but perhaps from the ashes of the resulting political and actual fires to come, there will be something left to salvage.
History will not forgive us nor should it.
Have a nice weekend.
= new reply since forum marked as read
