Pickling Process for all Types of Stainless Steel with recovering of material
Two step pickling process avoids waste and wastewater
The challenge in terms of sustainability:
Pickling of Stainless Steel is a necessary treatment to provide corrosion resistance. Objective was a pickling process equally applicable to all types of Stainless Steel, which enables dissolution of oxides with or without removal of base metal. The process should be applicable without waste and waste water, enable recovering of acid and metals and should not cause embrittlement.
The initial situation:
Presently available pickling processes can only be applied to a limited number of higher alloyed Stainless Steel qualities. Besides of hydrofluoric acid they use other acids like nitric acid and sulphuric acid. They affect environment by waste containing heavy metals and waste water containing noxios salts. Rinsed water, used acids and dissolved metals must be treated and discarded as hazardous waste with impact to environment.
The new pickling process POLINOX VA 100 only uses a solution of hydrofluoric acid in water. It is a two step process using the same acid concentration in each step. First step is an activation during some minutes followed without rinsing by the pickling process. The pickling solution contains a specially stabilised hydrogen peroxide in surplus.
The concentration of acid is determined according to the quality of Stainless Steel to be pickled, the desired speed of pickling and if oxides and Iron contamination should be removed with or without removal of base metal or with or without impact to the finish.
The treatment of rinse water and concentrates is done by neutralisation with lime milk. Hydrofluoric acid is participated as calciumfluoride and the metals as metal hydroxides. They are separated from the water by filtration. A two step neutralisation and filtration provides a separation of flourides and metal hydroxides, which can be reused. The filtrate is fed back to the rinse water system.
The sustainable strengths:
For the first time POLINOX VA 100 enables a high quality pickling treatment of all types of Stainless Steel, specially of low alloyed ferritic, martensitic or lean duplex without risk of hydrogen embrittlement.
Pickling can be applied selectively without affecting the surface finish or with removal of base metal. The speed of treatment compared to standard pickling processes at same acid concentration and temperature is at least 25% higher.
The process can be used wastewater free and does not need the relevant permissions from authorities. Acid and metals can be recovered as raw material for production of acid and Stainless Steel. This saves resources and avoids hazardous waste.
The process POLINOX VA 100 is free of mineralic acids and hydrogen embrittlement. It can be applied to all types of Stainless Steel starting at a Chrome content of 10%.
Dr. Olaf Böhme, Head of Research + Development
Brief profile of the company:
Name: POLIGRAT GmbH
Year established: 1954
Solutions: Surface technology for metal surfaces for improved functionality and appearance.
Internationality: Sites or distribution partners abroad
Sites abroad: United Kingdom, France, Hungary, Switzerland, USA, Canada
Distribution partners abroad: Australia, Belgium, Finland, India, Italy, Israel, Japan, Austria, Poland, Spain