Process overview


The Ash2Phos-process can be divided into two concepts (as can be seen in the picture above) depending on the size of the plant and its location i.e. a City-concept or an Industrial concept.

City concept

The city concept is an option for smaller ash volumes and stops with the intermediate products, which has to be upgraded to final products at an industrial site. To lower operation costs, waste acid (HCl) from the gas cleaning process of a waste incineration plant can be used in the Ash2Phos process to dissolve the ash. Since the city concept handles lower amounts of ash, produced waste acid is often enough to match the city concept's ash capacity. In addition to lower operational cost of the Ash2Phos process, the incineration plant saves input chemicals for neutralization and water cleaning of their waste liquid.

Industrial concept

The industrial concept produce commercial valuable products that are sold on the market today. The Ash2Phos process consists of 3 steps: a first acid step, a secondary basic step where intermediate products are produced, and finally a conversion step where intermediates are processed into final products.

The main input in the process are:

  • Ash from incinerated sewage sludge
  • Acid (HCl)
  • Lime

The outcome from the process are:

  • Recovered phosphorus, as ammonium phosphate (fertilizer, requires addition of ammonia) or calcium phosphate (feed additive). It is also possible, but less likely, to produce phosphoric acid and super phosphate fertilizer.
  • Iron as iron chloride or iron sulfate
  • Aluminum as aluminum sulfate
  • Residual sand (undissolved ash consisting mainly of silicates)
  • Heavy metal precipitate (for disposal)
The process itself

The process consists of several successive chemical reactions undertaken in room temperature. Only one of the chemical reactions benefit from a temperature of  40 degrees. There is no need for pressures and there is no need for exceptional materials in the equipment. The mass balance of the process is favorable where all input chemicals become part of the products.

Technical information regarding the phosphorus output products


Mono ammonium phosphate, MAP (technical grade)

  • Applications, fertilizer on agricultural field or in horticulture, feed ingredient
  • Quality, Technical grade 26,5% P (61% P2O5 and 12% N)
  • Cadmium content < 1mg Cd/Kg P ( Cd < 0,5 mg / Kg P2O5)
  • Efficiency in application, very high, the product is fully water soluble and plant available
  • Corresponds to CAS-nr: 7722-76-1

Ammonium phosphates is produced in two quality levels, fertilizer grade and technical grade. Fertilizer grade is the large volume phosphorus commodity and contains 21-22% P (48% P2O5) this product is not fully water soluble and contains impurities from the production process, gypsum etc. it also contains metals in relation to the content in the raw material and can only be distributed to the crop in solid form. As2Phos process always produce the highest quality i.e. technical grade, which is fully water soluble and can be used for fertilization in solid or liquid form.

Dicalcium phosphate, DCP

  • Applications, fertilizer on agricultural field or in horticulture, feed ingredient
  • Quality equal to today's products with a phosphorus content of 18% P i.e. 41% P2O5
  • Cadmium content < 1mg Cd/Kg P (Cd < 0,5 mg / Kg P2O5)
  • Efficiency in application, equal to today’s products
  • Corresponds cas-nr: 7783-28-0

Phosphoric acid

There is also an option to produce phosphoric acid, also with the same low cadmium content < 1mg Cd/Kg P ( Cd < 0,5 mg / Kg P2O5).

  • Corresponds cas-nr: 7664-38-2

Superphosphates

This option is less likely to be used, but single super phosphate or triple super phosphate can be produced. These products are lower grade phosphorus fertilizers that were more common in earlier days, but has now been replaced with ammonium phosphates.

Output of iron & aluminum


Iron

Two different products can be produced in the industrial concept from the intermediate ferric hydroxide.

Iron chloride, FeCl3

  • Application, flocculant for precipitation of phosphorus in waste water treatment plant
  • The product equals the today's commercial product
  • Correspond to cas-nr: 7705-08-0

Iron sulfate, Fe2(SO4)3

  • Application, flocculant for precipitation of phosphorus in waste water treatment plant
  • The product equals the today's commercial product
  • Correspond to cas-nr: 7782-36-0
Aluminum

Aluminum sulfate, AlSO4

  • Application, flocculant for precipitation of phosphorus in waste water treatment plant
  • The product equals the today's commercial product
  • Correspond to cas-nr: 10043-01-3

Output of residual sand & heavy metals


Residual sand

The remaining ash residue after dissolution

  • Washed sand that mainly contains silicates
  • The washed sand has possible application areas, such as, cement or filler in concrete.
Heavy metal precipitate

The heavy metals are separated as sulfide precipitate for disposal which will be disposed. Metal sulfides are chemically very stable and the sulfide precipitation is stat-of-the-art technology and widely used in many water cleaning applications.

Summary of the Ash2Phos process


A wet chemical process with following characteristics;

  • Recover phosphorus from sludge ash as high value products either as ammonium phosphates or as calcium phosphates
  • High phosphorus recovery rate >90%
  • Clean phosphorus products with a very low cadmium content <1mg Cd/kg P
  • Separation of other heavy metals for safe disposal
  • Recovery of iron & aluminum as precipitation chemicals
  • Favorable mass balance & low energy consumption since most of the process operates in room temperature.
  • Can also use sludge ashes with lower phosphorus content than from mono-incineration
  • Can use waste acids from sludge or waste incineration.

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