ABSTRACT
The production and recycling of lead acid batteries, has a very important role in the lead industry. The entire lead consumption from battery production is about 60—70% depending on a country, although recently the profitability is reducing due to environmental costs mostly in relation to waste generation and energy consumption. Very large amounts of toxic leachable soda slugs are produced for landfill from recycling spent batteries. Therefore developing a zero waste generating process to produce a new concept in the battery reprocessing industry is vital and which is the aim of this project.
In this project a scientific and rational model for the production of gypsum that was validated on a pilot plant scale. Therefore it was necessary to investigate how the variation in chemical composition will affect the synthetically produced gypsum quality, i.e. analyzing the gypsum produced for some trace metals, such as Pb, Fe, Cu, As, Sb, Zn, Ni, Cd and Na. Most of these metals can cause a serious hazard to humans through inhalation, skin contact, eye contact or ingestion [Rai and Amit, Jan 2002].
Na is not toxic however it can cause efflorescence and Fe causes discolouration of the plasterboard. Synthetic gypsum can be produced by a simple chemical reaction between sulphuric acid (H2SO4) and lime (Ca(OH)2) or limestone (CaCO3). The non-ferrous metallurgical industry produces large volumes of acidic effluents, or wastewaters, which are treated using lime neutralization in order to remove the acidity and heavy metals. The success of this research lead to investigating the possibility of making synthetic gypsum during the neutralization of acidic waste waters with lime or limestone. Gypsum samples were produced at different operational conditions (pH, temperature, mixer speed, residence time, etc.). The samples were analysed for trace metal content using flame atomic absorption spectroscopy and inductively coupled plasma spectrometry.
Ultrasound assisted crystallisation during the synthesis of gypsum was performed to observe the possibility of obtaining a cleaner gypsum product. A 40 kHz ultrasonic bath and a 20 kHz ultrasonic probe were used in this investigation. All the experiments performed in this investigation were lasted for 4 hours and were carried out at room temperature. Different ultrasonic powers and different methods of sonication methods were carried out at pH 2 and pH 4 in order to obtain the cleanest gypsum product. Various sonication methods were also carried out using the 20 kHz ultrasonic probe at 25%, 50% and 75% sonication powers.
