Recovery of gypsum from waste plaster board by recrystallization process

초록

We propose a recrystallization process for recovering granular crystalline gypsum from waste plaster board, and the operating factors were investigated. The waste plaster board was mainly made from Gypsum (90% or more), insoluble organic materials like paper (1-5%), and inorganic materials like quartz (1-4%). In the first stage of the process, the board was crushed in 2cm or less size and dehydrated in 75% or more dehydration rate. In the second stage of hydrating the dehydrated board, the needle-like gypsum in 15μm or less size were preferentially disintegrated from the board and recovered as under product in successive 325 mesh wet screening. In this case, the recovery of gypsum was affected by dehydration rate, solid concentration of hydration, agitation speed and hydration temperature. The experimental results showed that the optimum conditions for increasing gypsum recovery are as follows: dehydration rate of 75%, solid concentration at hydration of 20%, agitation speed of 250rpm, and room temperature. Under this condition, needle-like fine gypsum of 98.3% grade was recovered with 98.8% yield. This recovered fine gypsum was purified in the 3rd stage which is composed of dehydration in hot water of 97-99°C. It was then, made to undergo re-crystallization at 60°C for 5hours and 325mesh wet screening. In this stage, plate-like crystalline gypsum of 159μm medium size was obtained with 99.1% grade and 92.8% yield.

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