A Study on the Range of Ash Composition Suitable for High Quality Slag in Terms of Slag Strength and Leaching Characteristic of Pb and the Mechanism of Pb Leaching From Slag

For the purpose of promoting the beneficial use of molten slag obtained from municipal solid waste incineration ash, we investigated the strength of slag and the characteristics of Pb leaching in different ash compositions, identified the range of ash composition suitable for high quality slag, and elucidated the mechanism of Pb leaching from slag. The molten slag was produced by slowly cooling model incineration ash at a cooling rate of 4°C/ min, the composition of which was adjusted using a reagent. An abrasion test was used to estimate the material strength of the slag. The test results show the formation of Gehlenite crystals by precipitation, low abrasion loss, and high slag strength in the basicity (CaO/SiO2) range of 1.25 to 1.75. The results of the leaching test conducted in an acidic environment (pH 4.0) indicate that Pb leaching rates for eutectic compositions with basicity range of 1.0 to 1.25 are about 2 to 3 times higher than those for other ash compositions. The Japanese Leaching Test (JLT-46) indicates that most of the ash compositions with a basicity of 1.0 to 2.0 fulfilled the criteria for Pb leaching concentration. We conclude that the adequate ash composition is in the basicity range of 1.5 to 1.75 for high quality slag. Furthermore, the results prove that if the ash composition is the same, the amount of Pb leaching is proportional to the content of Pb in the slag under constant pH conditions.