Extraction of Phosphate from Waste Materials

  • ChemPubSoc Europe Logo
  • DOI: 10.1002/chemv.201700061
  • Author: Barbara Böck, Martin Bertau
  • Published Date: 05 September 2017
  • Source / Publisher: Chemie Ingenieur Technik/Wiley-VCH
  • Copyright: Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
thumbnail image: Extraction of Phosphate from Waste Materials

PARFORCE Technology is an industrial process for the extraction of phosphate from secondary raw materials. The acronym stands for "Phosphoric Acid Recovery From Organic Residues and Chemicals by Electrochemistry".


Dr. Barbara Böck, Editor-in-Chief of Chemie Ingenieur Technik (CIT), talked to Professor Martin Bertau, Freiberg University of Mining and Technology, Germany, about the development of this innovative industrial process which is capable of reintroducing phosphate into the substance cycle.

 

 

What was the motivation behind this study?

Well, let me begin with the fact that phosphorus is an essential element for life. That means it cannot be substituted by other elements and is inevitably essential in nutrition. It was in 2008, during the financial crisis, when the world was observing a dramatic price increase for rock phosphate material by roughly 420 %. Phosphoric acid is the main ingredient in any P-fertilizer, and consequently, such considerable price shifts will have an effect on basic food prices. People became aware of the vulnerability of the phosphorus supply, what prompted us to take a deeper look in this field.

Rock phosphate, which is the raw material behind all phosphorus chemistry, contains considerable amounts of heavy metals. Some of them are even radioactive. From colleagues in the phosphoric acid producing industry, as well as from the fertilizer industry, we knew that these impurities are a severe problem. In particular, this holds true for the German fertilizer ordinance, which sets clear maximum contents for certain metals.

 

 

Why was your attention focused on phosphorus and secondary raw materials?

Shortly after the price jump in spring 2008, an article was published that claimed that "peak phosphorus" would be reached in about 2030. Concerns arose that armed conflicts were a possible response to a dramatic phosphorus supply shortage in view of the world’s steadily growing population.

It only took a short glance at the relevant report of the geological surveys in the US, Britain, and Germany to unmask these concerns as nonsense. In fact, there is no basis for believing in "peak phosphorus". To speak frankly, phosphorus supply is secure at least for the forthcoming 300 years. Still, this discussion drew our attention to geopolitics and in its imponderabilities, and we began to investigate whether phosphorus supply can be maintained at satisfactory levels making use of domestic sources.

As a result, we identified secondary raw materials—which is a nice paraphrase for waste streams. Among these, sewage sludge incineration ashes (SSIA) soon emerged as a promising source for phosphate. I say phosphate because this is the chemical entity which bears phosphorus, in the form which is ingested and metabolized in living organisms.

SSIA have a much smaller heavy metal content than rock phosphate and, more importantly, contain no radioactive species. One cannot blame anyone for the high contents in natural rock phosphate material, which is recovered by mining. They are the result of phosphate deposit formation, which had taken place in the Cretaceous, about 70 million years ago. This is the so-called "geochemical heritage". This is where our SSIA come into play, since they are, as pointed out before, considerably less contaminated with transition metals. Phosphate in its diverse forms is a material that has in the past been traded for money. At present, though, it is simply disposed of, for the simple reason that there is a lack of technologies capable of reintroducing phosphate into the substance cycle. Thus, phosphate recycling stood at top of the list. If you take a look at the current list of critical raw materials by the European Commission, you will see it was the right time to get started.

 

 

Could you briefly explain your technology?

To cut a long story short, we looked for a technology that allows for recovering phosphorus from waste materials in a marketable form. In fact, the target product of choice is phosphoric acid, for which the entire market is open—well, with the exception of the food and pharmaceutical industries. And one can serve fertilizer markets, too, with phosphoric acid that is free of heavy metal impurities. At the end of the day, the solution was a process to produce the base chemical for the entire phosphorus chemistry. This is the PARFORCE process we have developed.

 

 

What is the main advantage of the process?

We are able to recycle phosphoric acid from secondary raw materials. What makes this technology so special is the broad range of feedstock suitable for P recycling as well as the quality of the product. The product is indistinguishable from primary phosphoric acid. In other words, the advantage is a real recycling product, which has the quality of a primary product, which can be traded worldwide, and which is a starting material for any phosphorus chemistry.

 

 

What distinguishes your work from other methods to gain phosphorus?

In Germany, there had been numerous activities underway since the very late 1990s. However, none of them was able to produce phosphoric acid. As a matter of fact, the vast majority of phosphate recycling projects was focusing on producing either fertilizer, or their products were inorganic phosphate salts, such as the phosphates of calcium, magnesium, iron, or aluminum, as well as magnesium ammonium phosphate. They are water-insoluble and, thus, exhibit little to no bioavailability.

More importantly, 85 to 90 % of a SSIA is an inorganic residue, for which a use has to be found. Phosphate recycling to fertilizers appeared attractive for a long time since the residual inorganic fraction could be distributed on the fields along with the phosphate recycling product, provided the material is in accordance with the fertilizer ordinance. However, typically there has been too little attention to legal restrictions and equally to economic factors. From a legal point of view, the recycling product has to be classified by the authorities as non-waste material, it has to have product status, and must be certified as a fertilizer. In addition, many projects were far from being economical. For these reasons, we focused on phosphoric acid instead of fertilizers.

 

 

How long did the project take from the first idea to the real process?

We started in 2009, that is eight years so far. Looking back, it took four years to develop the process on a laboratory scale. In the following two years, we brought the process to TRL 5, which is the small-scale production of phosphoric acid in a mini-plant with 20 L-vessels. In that time, we found that the results were so promising and that the chemistry was so reproducible and robust that we decided to apply funding for a start-up-project. And we were successful.

In the meantime, the Federal Minister of Economics and Technology had awarded us the resource efficiency prize and we were awarded the IQ-Innovation prize by the German chemical industry and Central German Chambers of Industry and Commerce. Since March 2016, we have been receiving funding from the Federal Ministry of Economics within the EXIST!-programme as well as from the Saxon Ministry of Science and the Arts with the aim to establish a demonstration plant at TRL 7. I would like to take the opportunity to express my thanks for this support.

At present, we are a team of four, in addition to myself, who is in the process of founding the start-up company, which is engaged with phosphorus recycling, out of university.

 

 

What is the broader impact of this technology for the scientific community?

These last eight years have shown that scientific progress is far more than gaining knowledge. Our activities have experienced a huge, fascinating momentum of its own, and I think the step towards founding a start-up company from university research is done too infrequently. I must confess, it is a great experience to see your very first lab bench experiments grow up to a commercially viable process which I would not want to miss.

 

 

How will you follow up on this discovery?

Well, that’s, in fact, our start-up company. At present, all that I can say is that our demonstration plant will go into full operation in September 2017. From then on, we will be able to process one tonne of starting material per day, producing up to 400 kg of phosphoric acid. Of course, we steadily have been extending the range for the starting materials suited for the PARFORCE process, and we will continue doing so.

 

 

Why did you choose this technique?

This is easily answered: Because it allows us to produce pure phosphoric acid, up to food grade from a broad range of secondary materials.

 

 

How big an impact do you see your work potentially having?

Industry will be using phosphate as a recyclable raw material far more effectively. Unlike earlier times, valuable resources will no longer be disposed of, and the use of heavy-metal charged primary phosphoric acid in fertilizer production can be reduced.

 

 

Which part of your work proved the most challenging?

Oh, different parts. What was most challenging was filtration, digestion, acid recycling, and product acid purification.


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