Jacobs Journal of Civil Engineering

Distribution of Acid-Extractable Pb Contents in Molten Slag From Municipal Solid Waste Incineration Ash

*Satoshi Mizutani
Department Of Civil Engineering, Osaka City University, Japan

*Corresponding Author:
Satoshi Mizutani
Department Of Civil Engineering, Osaka City University, Japan
Email:miz@urban.eng.osaka-cu.ac.jp

Published on: 2016-03-28

Abstract

In Japan, when molten slag from municipal solid waste incineration ash is used in the general environment, acid-extractable Pb contents must be lower than utilization criteria, as determined by JIS (Japanese Industrial Standard) K 0058-2 method. However, representativeness of 1,000 t of slag samples in practical usage is ineffective because only 6 g of samples are used for testing under such standards. This study has three aims: 1. to determine the variation of acid-extractable Pb contents in the 20 slag samples from one plant, 2. to estimate the probability of excess acid-extractable Pb content distributed among the 20 samples that adhere to utilization criteria, and 3. to show the importance of evaluating acid-extractable metal contents not based on a single analyzed value but probability density. In this study, twenty lots of slag were sampled from one melting plant for two months in 2006. In the first experiment, 6 g of samples were taken from each lot at random and tested. In the second experiment, 20 portions were prepared from four lots of them and 20 of 6 g samples were taken from each small portion and tested. The results indicate that significantly high Pb values derived from heterogeneous character. The dataset shows a log-normal distribution and the rates exceeding the utilization standard are discussed based on probability density function.

Keywords

Molten Slag; Pb; Distribution; Acid-Extractable Content; Log-Normal Distribution

Introduction

Approximately 200 facilities for melting municipal solid waste (MSW) or municipal solid waste incineration (MSWI) ash are running in Japan and more than 800,000 t of melting slag are generated annually [1, 2]. The molten slag is glassy and stable materials, and it is expected to be used in various civil engineering projects [3]. However, the molten slag may contain heavy metals derived from solid waste. For this reason, two test methods were conducted to determine heavy metal content on the basis of separate criteria: acid-extractable content and leaching behavior, which are outlined by JIS (Japanese Industrial Standard) K 0058-2 [4] and JIS K 0058- 1 [5], respectively. Utilization criteria of molten slag for hazardous elements are shown in Table 1. Generally, with regard to MSW molten slag, the analysis and the confirmation of Pb contents is very important essential because concentration levels often exceed the utilization criteria.