Paolo Bevilacqua

The influence of particle shape on the dynamic dense medium separation of plastics

Abstract The separation of post-consumer plastics of different polymeric compositions is becoming an important topic for the reduction of waste and promotion of recycling. The comminution of plastics creates variable particle shapes which cause difficulties in the separation by a cyclone. To study the influence of particle shape, tests have been performed to determine how the partition curve changes with particle shape in cylindrical cyclones. The test results give a complete picture on the influence of particle shape and size on the cut density d 50 and the probable error E p . Coupled with a mathematical description of the partition curve, these parameters can assist in process simulation, selection and design of dense medium separation (DMS) systems devoted to plastic recycling.

Modelling the throw of metals and nonmetals in eddy current separations

Abstract The trajectories of real scrap particles processed with an eddy current separator are compared to computer simulations to investigate the effects of particle shape and particle–particle interaction, effects that are difficult to catch in a purely theoretical model. The results show that the primary particle parameters are size, conductivity and initial orientation, provided that the size of a particle is defined in relation to the eddy current process. Therefore, the detailed shape of scrap particles is less important. The effects of particle–particle interaction on the grade and recovery can be predicted by considering two different types of collisions between nonferrous and nonmetal particles. This results in a simple theory that can be incorporated into a simulation model.

Eddy Current Separation of Fine Non-Ferrous Particles from Bulk Streams

Recovery of fine non-ferrous metals from waste streams is a notoriously difficult problem in eddy current separation technology. Existing processes either have a low capacity or an incomplete recovery for particle sizes below 5 mm. In a new process, the particles are fed slightly wet to make them stick to the surface of the conveyor belt. The action of the magnet rotor makes the non-ferrous particles tumble, so that they break loose from the belt and end up in front of the rotor. The new process combines a relatively high capacity with an almost complete recovery, even for heavy and poorly conducting non-ferrous metals.

Comminution of porous materials

Abstract The behaviour of porous materials in comminution processes differs substantially from that of non-porous materials. It is strongly affected by the type of porosity, which may be characterized by different void shapes and interconnection degrees. This paper discusses the comminution of porous materials having voids of compact shape (like spheres) and not interconnected. For such materials different behaviours can be expected for the two comminution ranges above and below the mean voids interspace. In fact, for the coarser sizes the mechanical behaviour of the material is that of the porous material defined by its bulk mechanical properties; below the mean voids interspace down to very fine sizes the mechanical behaviour of the material is that of the non-porous material constituting the matrix. Therefore, a transitional region should exist, with the result of bi- or trimodal size distributions for comminuted porous materials. To verify the above mentioned theory, tests were performed on two types of materials, artificial and natural: (a) perforated bricks with 20 mm voids; (b) natural pumice stone. The resulting size distributions differ in slope above and below the mean voids interspace, and the two parts of the distribution are connected by a transition curve. The results may be of interest in studying the comminution of different types of materials, particularly secondary materials and scraps.

Rheology of Low Density Suspensions in Dense Medium Separation of Post-consumer Plastics∗

Abstract The aim of this paper is to investigate the feasibility of using clay suspensions in dynamic dense medium separation of post-consumer plastics. The Theological behavior of suspensions formed with different commercial clay samples was studied to ascertain that both viscosity and stability could be maintained in the range required by dense medium separation systems. Suspensions made with a selected clay sample were used in a laboratory test rig equipped with a conical cyclone and a cylindrical cyclone with peripheral underflow discharge. Preliminary separation tests were carried out using different density plastic tracers. The results with both separators demonstrated that the separation of two plastics of different densities can be obtained.

Liberation of voids by comminution : its influence on apparent density of porous materials

Abstract For the first time, the concept of liberation of voids in a porous material is defined. A simple model has been developed for calculating the degree of liberation of voids for different sizes of the particles resulting from comminution. Void liberation affects the apparent density of the particles, i.e. the most important particle characteristic in gravity separation processes. This paper shows to what extent the porous material should be reduced in size to obtain an adequate liberation for the process requirement.

Size distribution of comminuted porous materials: the oops region

Abstract This theoretical paper examines the expected shape of the size distribution curves of comminuted porous materials. A transitional region is predicted in the size distribution of the fragments from porous materials called the ‘oops’ region. Also predicted is a change in fragment shape before and after the particle size passes through the size region of the voids—the Swiss cheese effect. The problem of void liberation and characterizing or measuring void volumes is discussed.

“The Italian Job”: Approaching and Tackling Diffuse Soil Pollution in the EU and the Italian Context

Diffuse soil pollution is an example of damage caused by human activities and can be understood in the urban context as a combination of causes due to the presence of various and multiple sources of contamination, such as: car traffic, industrial activities and heating. Importantly, the steadfast expansion of city districts over time has brought either industrial activities to enclose residential areas or (although in a few cases) neighborhoods to envelop previously highly industrialized areas. In Italy, both phenomena represent a widely acknowledged reality, e.g., the municipalities of Taranto and Trieste.Yet, despite the widespread awareness of the impact of this form of pollution on natural resources and human health, EU environmental legislation depicts an overall picture of fragmentation and poor coordination. Thus, Italian local administrations are striving to devise appropriate methodologies and planificatory measures to bridge such regulatory gap and ultimately find an adequate and comprehensive solution to the problem.

Multiobjective Optimization, Scalarization, and Maximal Elements of Preorders

We characterize the existence of (weak) Pareto optimal solutions to the classical multiobjective optimization problem by referring to the naturally associated preorders and their finite (Richter-Peleg) multiutility representation. The case of a compact design space is appropriately considered by using results concerning the existence of maximal elements of preorders. The possibility of reformulating the multiobjective optimization problem for determining the weak Pareto optimal solutions by means of a scalarization procedure is finally characterized.

Existence of Order-Preserving Functions for Nontotal Fuzzy Preference Relations under Decisiveness

Looking at decisiveness as crucial, we discuss the existence of an order-preserving function for the nontotal crisp preference relation naturally associated to a nontotal fuzzy preference relation. We further present conditions for the existence of an upper semicontinuous order-preserving function for a fuzzy binary relation on a crisp topological space.