Resources, Conservation and Recycling 34 (2002) 193–207 The description of solid wastes by particle mass instead of particle size distributions H. von Blottnitz a, *, A. Pehlken b , Th. Pretz b a Department of Chemical Engineering, Uniersity of Cape Town, Priate Bag, Rondebosch 7701, South Africa b Chair for Processing and Recycling of Solid Wastes, Aachen Uniersity of Technology, Templergraben 55, D-52056 Aachen, Germany Received 3 April 2001; accepted 4 September 2001 Abstract The theory and practice of processing of solid wastes for recycling and treatment needs more rigorous approaches in areas such as the development of sampling protocols, quality control and process modelling. For solid wastes, which consist of mixtures of particulates, certain parallels may be drawn to the discipline of mineral processing, in which the application of a mixture of semi-empirical knowledge and fundamentals is common and shows great benefits. A fundamental building block in such approaches is the ability to describe particle size distributions (PSD) mathematically. Previous attempts to transfer this tool to the field of wastes have not produced meaningful results, for a number of reasons discussed in the paper. At a more fundamental level, it can, however, be recognised that PSDs used in mineral processing are mostly used for convenience (they can be rapidly determined), with the parameters of real interest, yield and grade, expressed as weight fractions. The same is observed in sampling theory, where size is used to estimate parameters that have mass units. From this perspective, it is proposed that it would be possible to use mass distributions in a semi-empirical form in the description of solid waste processing technology, on condition that regular features can be observed in the distributions of masses of definable particle classes in solid waste mixtures. This possibility is explored from a theoretical perspective, and some experimental evidence is presented in support of regularity, both in mixtures of re-granulated plastic wastes, and in a residual solid waste product from a bio-mechanical treatment plant. Particularly, the concept of unit mass distribution is defined and found to be described adequately by a modified Rosin–Rammler–Sperling– Bennett (RRSB) function. © 2002 Elsevier Science B.V. All rights reserved. www.elsevier.com/locate/resconrec * Corresponding author. Tel./fax: +27-21-650-2512. E-mail address: hvb@chemeng.uct.ac.za (H. von Blottnitz). 0921-3449/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0921-3449(01)00107-0