Showing papers by "Carlos Negro published in 2001"

Free acids and chemicals recovery from stainless steel pickling baths

Abstract: The conventional process used to treat waste acids from the stainless steel pickling baths is a direct neutralization with alkali. However, this process requires a high consumption of chemicals, produces a large amount of solid wastes, and furthermore, does not meet the recent European Waste Treatment Regulation because of the nitrogen contained in the final effluent. This paper presents an alternative treatment method based on a diffusion dialysis process for the free acid recovery and a neutralization process, followed by a salt splitting process, for the chemical recovery. This alternative eliminates waste disposal problems and, at the same time, it regenerates and recovers valuable by-products, which contributes to the economic feasibility of the process. Therefore, the work presented is focused on the technical and economical feasibility of electromembrane processes for the European spent pickling baths. Furthermore, bipolar electrodialysis and membrane electrolysis systems are compared for the salt ...

Recovery of the Metals from Pickling Liquors of Stainless Steel by Precipitation Methods

Abstract: Pickling liquors are still one of the main environmental concerns of the stainless steel industry. Most of the processes designed to recover these wastes focus on the recovery of their acid content (mixtures of HF and HNO 3 ), but also produce metals (iron, nickel, chromium and molybdenum) as a low quality by-product that sometimes must be treated as a residue. This paper presents the development of a process to obtain commercial products from the metal content of these liquors. To this end, three precipitation methods (total, sequential and modified) were tested. The proposed procedure is the last one, i.e., modified precipitation. It consists of two stages each resulting in the recovery of solids. The first product is mainly composed of iron and chromium hydroxides and oxides, along with molybdate, while the second is mainly composed of nickel hydroxide. In addition, this method allows an almost total recovery of the acids.

Destabilisation of dissolved and colloidal material derived from coated paper

Abstract: There is a clear need in papermaking, and recycled fibre mills, for quantitative identification methods to determine contaminants and potential deposit formers contained in the raw materials. This paper presents a new reliable method for determining the tendency of dissolved and colloidal material to form deposits. One of the main problem materials is the coating chemicals. In this research the influence of different coating formulations, types and doses of destabilisation additives, and process conditions on deposit formation are studied.

Novel process to recover by-products from the pickling baths of stainless steel

Abstract: Development of an integrated process (the PIBARE process) which is able to recover and recycle free and complex acids back to the pickling tank is described. The recovery of these by-products proceeds while the metals are recovered in the form of electrodeposited metal alloy and are internally recycled to the stainless steel manufacturing process. Virtually no solid residue or liquid is produced in the process. Results after three years of investigation are very promising, having achieved all stated objectives at least on the laboratory scale. The new technology promises significant economic and environmental benefits over other existing technologies for the treatment of spent baths. However, since the benefits have not been confirmed at the pilot scale, commercial application would require additional research, including finding more efficient and more selective anionic membranes. 3 tabs., 6 figs.