C. Negro

Waste management from pulp and paper production in the European Union

Eleven million tonnes of waste are produced yearly by the European pulp and paper industry, of which 70% originates from the production of deinked recycled paper. Wastes are very diverse in composition and consist of rejects, different types of sludges and ashes in mills having on-site incineration treatment. The production of pulp and paper from virgin pulp generates less waste but the waste has similar properties to waste from the production of deinked pulp, although with less inorganics. Due to legislation and increased taxes, landfills are quickly being eliminated as a final destination for wastes in Europe, and incineration with energy recovery is becoming the main waste recovery method. Other options such as pyrolysis, gasification, land spreading, composting and reuse as building material are being applied, although research is still needed for optimization of the processes. Due to the large volumes of waste generated, the high moisture content of the waste and the changing waste composition as a result of process conditions, recovery methods are usually expensive and their environmental impact is still uncertain. For this reason, it is necessary to continue research on different applications of wastes, while taking into account the environmental and economic factors of these waste treatments.

Enzymatic approaches in paper industry for pulp refining and biofilm control

The use of enzymes has a high potential in the pulp and paper industry to improve the economics of the paper production process and to achieve, at the same time, a reduced environmental impact. Specific enzymes contribute to reduce the amount of chemicals and energy required for the modification of fibers and helps to prevent the formation or development of biofilms. This review is aimed at presenting the latest progresses made in the application of enzymes as refining aids and biofilm control agents.

Mechanism and kinetic control of the oxyprecipitation of sulphuric liquors from steel pickling

Abstract Steel pickling liquors are one of the main environmental problems of steel making. Currently, there are several processes for the treatment of sulphuric liquors, although most recover only acid and haematite (α-Fe 2 O 3 ). We propose an oxyprecipitation process for this recovery, allowing several kinds of iron oxide or oxyhydroxide to be obtained. The aim of this paper is to determine the kinetic control and reaction mechanism. The influence of different variables is evaluated and two experimental ranges for the synthesis of goethite (α-FeOOH) and magnetite (Fe 3 O 4 ) are defined. A systematic study is carried out in these experimental intervals, and the results are analysed in order to determine the reaction order and the type of kinetic control. Finally, from these data, morphological and crystallinity studies and new experiments, the reaction mechanism is proposed.

Optimization of Pitch Removal by Dissolved Air Flotation in a Eucalyptus Kraft Mill

Abstract Wood extractives cause production and environmental problems as well as decreasing the quality of the final product in pulp and paper manufacturing. These disturbances are commonly referred to as pitch problems in this industry. The complex composition of wood extractives is the reason why the nature of pitch problems is different for the various wood species. Also, there is a strong dependence on pulping, bleaching, and papermaking processes. Nowadays, the most common way of handling pitch is to use chemicals in order to fix the extractives to the fibers and thus remove them from the process with the final product. However, this causes serious problems in the final product and also increases problems when paper is recycled. Thus, fixation is not considered to be a sustainable operation for the future. Alternative methods to remove the extractives from the process water must be developed to overcome pitch disturbances and increase pulp quality. This is especially important in mills with closed water loops where the accumulation of extractives in the process waters can occur. In this paper an internal process water kidney, based on dissolved air flotation (DAF), is considered. The objective was to remove extractives from a kraft mill process using Eucalyptus globulus as the raw material. The results show that with the dual system, polyethylene oxide and phenol formaldehyde resin (PEO/PFR), it is possible to remove 80% of the extractive compounds by DAF. Three different techniques, hemacytometry, gas chromatography and turbidity measurement, were used to evaluate the removal efficiency. The applicability of a fast measurement, such as turbidity, to optimize the DAF operation during a future mill operation was studied. This research was carried out within the European Pitch Project (QLK5‐CT‐1999‐01357) funded by the European Commission. The authors wish to thank Beatriz Rodriguez for her skillful laboratory work and the personnel of ENCE pulp mill in Pontevedra for their cooperation.

Mathematical model of magnetite synthesis by oxidation of sulfuric pickling liquors from steelmaking

The aim of this paper is to propose a model obtained through experimental design which represents the synthesis of magnetite by oxidation-precipitation of sulfuric liquors from steel pickling. The studied variables are pH (5.5 - 6.5), stirring speed (250 - 1,000 rev * min-1) and flow of air used as oxidizer (5 -10 l * min-1). The model is valid within the experimental ranges and for a temperature of 70 degrees C. The proposed model is validated through statistical methods. The influence of each variable is studied related to the reaction mechanism and the optimal value of each one is determined.

Treatment and recovery of pickling liquors

Abstract The aim of this paper is to present the scientific and technological techniques available for the treatment and/or recycling of waste liquors from steel pickling processes in the steelmaking industry. Due to their high iron and acid contents, pickling liquors are a source of environmental pollution. The production of this type of waste is estimated at 100 1/t steel. Because of their pollutant content and corrosiveness these liquids appear in the list of hazardous wastes in all legislations. In US legislation (US Resource Conservation and Recovery Act. Public Law 94–580) they appear with number K062. When seeking to resolve the environmental problems associated with this type of waste two main options are available: that of applying treatments which aim to neutralize the waste or that of recycling the different components which make up the liquors. In this second case the aim should be to recover the acid which can be recycled in the pickling baths and to recover the iron, obtaining products with ...

Protocol for the synthesis of Ba-hexaferrites with prefixed coercivities

Abstract The ferrite industry is one of the largest consumers of iron oxides, usually in the form of hematite from the roasting of steel pickling liquors or from mineral sources. In previous papers we have tested an oxidation process for obtaining magnetite and goethite from steel pickling liquors and two mathematical models have been proposed for synthesizing these two iron oxides. In this paper, the characteristics of magnetite and goethite are related with the coercivity of hexaferrites synthesized when the former are used as raw materials. Constant conditions were used for the ceramic method. Using goethite, Ba-hexaferrite is obtained only when the goethite is precipitated at the lowest oxidizer flow. When magnetite is used, a protocol with a statistically validated correlation is proposed for synthesizing hexaferrites with coercive fields between 230 and 450 kA/m. This correlation is valid for an oxidation process carried out at stirring speed of 1000 rev/min and with an air flow between 7.5 and 101/min. A second empirical correlation is proposed for obtaining final coercivities between 450 and 525 kA/m, for which it is necessary to increase the calcination time.

Synthesis of M-type hexaferrites from steel pickling liquors (ID 109)

Abstract The recovery of steel pickling liquors is one of the main environmental aspects that the steelmaking industry must resolve. We propose the synthesis of barium M-type hexaferrite from these liquors as a recovery treatment. Two methods of synthesis have been studied: a variation of the ceramic method, and an oxicoprecipitation process. Products with excellent magnetic properties have been obtained.

Improvement of ceramic method for synthesizing M-type hexaferrites

Abstract The aim of this paper is to improve the standard ceramic method for the synthesis of hexaferrites, studying several alternatives to the usual raw materials of iron and barium oxides and new ways of developing the wet-milling. The research has been focused in the two first stages (the so-called red-milling and the presintering or calcination step) of this process, optimizing their variables. They are type of milling-fluid, temperature and time of calcination, heating rate and BaO/Fe2O3 molar ratio. The optimization variable was the coercive field. The use of iron oxides different than α-Fe2O3 yields hexaferrites with magnetic properties higher than commercial ones. Thus, these hexaferrites are optimum as permanent magnets and can replace other more expensive magnets.

KINETICS AND MECHANISM OF THE OXYPRECIPITATION OF WASTE HYDROCHLORIC PICKLING LIQUORS

Abstract The aim of the research project presented in this paper is to devise a process to treat waste liquors from the pickling of iron or steel with hydrochloric acid in rolling mills, recovering the high iron content in the form of oxides or oxyhydroxides which can later be used in other industrial processes. In addition to reducing water pollution, such a process attaches a new value to this ferrous waste. Chlorinated liquors are oxyprecipitated, leading to the formation of different combinations of iron oxides and oxyhydroxides, with the total removal of Fe+2 and the production of ammonium chloride solutions easily broken down into hydrochloric acid and ammonia. The precipitates have different industrial outlets, making the oxyprecipitation process an attractive solution for the treatment of waste pickling liquors.