Showing papers by "Carlos Negro published in 2005"

Effect of Shearing Forces and Flocculant Overdose on Filler Flocculation Mechanisms and Floc Properties

Abstract: The increasing use of fillers makes filler retention a more critical issue. The effects of both shearing and flocculant overdose on filler flocculation kinetics and mechanisms and floc properties, ...

Flocculation mechanism induced by phenolic resin/PEO and floc properties

Abstract: The flocculation of an industrial furnish of TCF Kraft bleached pulp and ground calcium carbonate, induced by polyethylene oxide, and by the dual system formed by polyethylene oxide (PEO) and formaldehyde-phenol resin (PFR), was investigated and compared in order to study the flocculation kinetics, the flocculation mechanism and the properties of the formed flocs. A technique based on the measurement of the particle chord size distribution, called focused beam reflectance measurement, was used to carry out the research. The ability of the polyacrylate contained in the commercial ground calcium carbonate as a PEO cofactor was observed. Results confirmed the formation and the coacervation of the complex PFR-PEO, which loses its flocculant properties over time, confirming the complex bridging flocculation model. The shearing forces effect on the flocculation kinetics and on the properties of the formed flocs was also studied. © 2005 American Institute of Chemical Engineers AIChE J, 51: 1022–1031, 2005

Nickel hydroxide recovery from stainless steel pickling liquors by selective precipitation

Abstract: Stainless steel pickling liquor is obtained when a steel surface is treated with hydrofluoric and nitric acid mixtures. Industrial treatments of this dangerous and toxic effluent are focused on acid recovery, while metals are considered as a waste to be managed. Thus, a process taking into account the need to recover valuable metals is under development. This work presents the optimization of the first precipitaiton stage of this new process, with the aim of separating metals (iron and chromium) as fluorides by crystallization, keeping nickel in solution. Experimental conditions that lead to the best yield of reaction were 60−65 °C, pH 4.1−4.2, and free fluoride from 14 to 15% of alkali stream as potassium fluoride. Crystals obtained are mainly hydrated K2FeF5 and CrF3, with a little fraction of other oxides and fluorides phases. The entire content of nickel remaining in solution precipitates as Ni(OH)2 in another stage.

Study of Filler Flocculation Mechanisms and Floc Properties Induced by Polyethylenimine

Abstract: The research on filler flocculation and floc properties induced by polyethylenimine was carried out by monitoring the particle chord length distribution during the flocculation, deflocculation, and reflocculation processes for different polymer doses. Results show that there are two PEI doses that produce a maximum flocculation due to different flocculation mechanisms. Low PEI doses induce a fast flocculation through bridge formation, but high PEI doses induce a slow flocculation by charge neutralization. The proposed flocculation mechanisms, presented in this paper, explain the observed floc properties and their dependence on the polymer dosage. As the flocculation mechanism determines the floc properties and, therefore, the nature of the retention and drainage processes, the findings may allow papermakers to improve the optimization of the wet-end processes by controlling the PEI dosage more accurately. The study of flocculation kinetics and floc stability showed that the optimal dosage point depends st...

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 wa...

Breaking load and bending strength prediction in manufacture of fibre cement composites using artificial neural networks and a flocculation sensor

Abstract: The optimisation of the flocculation process during fibre cement production is a new key issue for the fibre cement industry. Many companies face difficulties in optimising the flocculant dosage in real time, which leads to product strength losses. This paper shows the feasibility of using artificial neural networks (ANNs) to establish correlations between flocculation data, in-line measured in a Hatschek machine by a focused beam reflectance measurement (FBRM) sensor, and mechanical properties of final composites. The results show a clear relationship between the mechanical properties of fibre cement composites and the flocculation process and that these are determined in real time. Three ANNs have been created to predict breaking load for 48 h and 7 days and bending strength for 7 days, to obtain good correlations between the predicted and the real values.

Pitch Control in Thermomechanical Pulping and Papermaking by Enzymatic Treatments

Abstract: Colloidal wood resin can become unstable in pulp and papermaking processes forming pitch deposits that affect both runnability and product quality. Enzymatic treatments can degrade triglycerides to fatty acids, which may affect the deposition tendency of the resin. In this paper, the effects of enzymatic treatment of wood resin in TMP were studied using four modified lipases. At 60 C the unmodified Resinase hydrolysed 90% of the triglycerides and reduced the amount of deposit, but the efficiency decreased at higher temperatures. With the most thermostable modified Resinase it was possible to hydrolyse 72% of the triglycerides even at 85 C, which is very important for industrial applications. Despite the efficient enzymatic hydrolysis of the triglycerides, the deposition tendency of the colloidal wood resin was not always reduced.

Electrochemical treatment of straw weak black liquor from a kraft pulping plant

Abstract: An electrochemical treatment can be applied to remove lignin from the weak black liquor (WBL) from pulping plants, concomitantly with sodium salts' convertion into caustic soda, that can be reused in the pulping process or in other sequences, depending on the required. concentration. The electrolytic processing of kraft weak black liquor from a pulp mill, using straw as raw material, was studied at laboratory scale in a batch mode. The main problem found was anode's. high fouling, which was solved by using platinum wire anodes in combination with high current density through the anode and turbulent flow of the WBL in the anode compartment. To avoid anode's fouling, the velocity of the WBL in the cell was critical, while current density and temperature optimization were critical for the economical viability of the process.