Central oparbejdning af galvanisk affald
This present project has been carried out in 3 main steps. Step 1 has aimed at the collection of experiences within the particular field. The purpose of Step 2 (the phases 2,3, 4 and 5) has been to identify a suit-able interface between the producer and the central waste treatment plant and to document that the identified interface is realistic and able to control in practice. Step 3 (phase 6) is a Feasibility Study, the purpose of which has been to define a basis of decision for the implementation of a central treatment plant under the given conditions.
The project has gradually been developed during the projecting phase as a result of the influence from the interesting parties on the original project objectives and as a result of changing outward circumstances. The results of the project work can thus be listed as follows:
In 1996 we were introduced to the Russian company ERG, which had developed a method for treatment and recovery of galvanic waste. This was demonstrated on laboratory scale at ERG and it was very convincing. Even though we could not gain access to the only Russian full-scale plant, operating after the principals of the ERG-method, it was decided that ERG should prepare a proposal for a Danish recovery plant for heavy metal waste.
In the start emphasis was put on the technology, in particular on the types of products to be produced from the different waste fractions. More products lead to the better plant flexibility, which is of importance for the plant's stakeholders and economy.
To facilitate ERG's work there has been made a prognosis of the total amount of heavy metal waste volume from the metal finishing industry in Denmark. Waste is the potential raw material for the plant. Of course the plant cannot expect to receive all the Danish waste for recovery, as already today a minor part of this waste is sent abroad for recovery. It is possible that the plant on a long-term basis will receive heavy metal waste from other branches as well, but this aspect has not been covered in the project.
The waste prognosis for year 2000 indicates that from the metal finishing industry in Denmark alone will be approx. 2000 tons of heavy metals in the waste, comprising nickel, chromium, copper, zinc, tin, iron and aluminum. Iron makes up 50% of the total, while zinc not unexpectedly account for 25%. Hereafter copper, aluminum, chromium, nickel and tin. The waste prognosis shows that the hot dip galvanizing industry generates 53% of the heavy metal waste, while the electroplating industry only 9%.
On the basis of this waste prognosis ERG has proposed a solution, which utilizes the various waste fractions the best possible way. It is a comparatively simple process, which concentrates mainly on the utilization of iron, zinc, copper and chromium, which all are present in the waste in rather large amounts. These compounds will have to be re-covered to simple main products, which can easily be sold at a fair price.
It is estimated that approx. 5900 tons of a mixed iron-zinc-phosphate pigment for corrosion protection paint can be produced a year. Furthermore it is estimated that 2700 tons of pure iron (III) hydroxide can be extracted and recovered to various products. The copper is easily transformed into copper sulphate; estimated production 700 tons a year. Finally, 145 tons of chromium hydroxide are predicted to be produced on a yearly basis, which can be recovered to other applicable products. It might be considered before initiation of the plant or at a later point of time to produce more sophisticated products out of these main compounds.
Aluminum, nickel and tin are only present in relatively small quantities, which is less interesting. ERG has suggested that these metals are recovered as hydroxides and then further processed.
ERG has not described the processes and the construction of the plant in details in the draft project, as the company does not want to reveal the process for fear of somebody will steal the idea. Therefore, at this point of time we will have to settle with a rough description. This description shows the process is based on a relatively simple inorganic process, where the metals successively are extracted from an aqueous suspension by adjusting the pH and adding various chemicals.
The equipment is ordinary chemical process equipment and the design and construction of the plant seems rather straightforward. Therefore it will probably be much cheaper to establish the plant than estimated. ERG has presumed that a Danish plant needs 10,000 mē floor for various indoor activities exclusive possible indoor storage space.
The greatest advantage of ERG's method is that it is possible to re-cover both liquid waste and solid sludge with mixtures of several metals. The process is based on a mixed sludge of one or the other com-position, but leaving the possibility of adding pure waste fractions at a later stage in the process, when some preliminary separations of the "starting mixture" has been carried out.
ERG has made laboratory tests with 5 different types of characteristic Danish "galvanic sludge" and the results have roughly met the expectations. It is possible to achieve products with an acceptable degree of purity of iron, zinc, aluminum, copper, chromium, nickel and calcium. The samples contained so little tin that there was no basis for recovering it.
If such a plant is established in Denmark it will provide unique possibilities of recovering mixed metal hydroxide sludge from the many chemical precipitation plants in the metal finishing industry. This will enable each individual enterprise to make CT-solutions on the basis of heavy metal sludge from their own existing wastewater treatment plant. Implementation of other CT-solutions can then be made if necessary in the production where it will be financially or environmentally advantageous.
Construction of a treatment plant for galvanic waste based on ERG's method has just been initiated in Kaliningrad. This project is supported by DEPA. The experiences from this plant will provide us with sound documentation of the concept operating in practice, to be used in the projecting of a future Danish treatment plant.
The project is now in the hands of interested parties and potential investors to determine whether our project proposal shall be scrutinized further, in preparation for a Danish recovery plant for heavy metal waste.
We will clearly recommend that this project is further evaluated, as we obviously here have discovered a unique method, unknown to us until now.