Feasibility of Manufacturing Building Materials by Recycling a Waste from Ion Exchange Process

Abstract

In this paper, Cd²⁺, Cr³⁺ and Pb²⁺ pre-exchanged tuff has been used in mixtures with lime and gypsum in order to assess the potentiality of this type of binding system for the manufacture of pre-formed building elements. Exchanged zeolitic tuff can be obtained as a solid waste from ionic exchange processes of industrial acid wastewaters containing heavy metals. This type of treatment can be a cheaper alternative to traditional precipitation processes and this work has the scope to assess the feasibility of recycling the exchanged tuff from both the technological and environmental points of view. Experiments were carried out to study the effect of the above heavy metals on the hydration behaviour and mechanical strength of the hardened products. To this regard, curing at 40°C for up to 28 days gives in all cases unconfined compressive strength higher than the minimum value required in Italy for pre-formed building elements. From the environmental point of view, three tests have been used for the assessment of leaching behaviour of the hardened samples. The three tests are the TCLP, US-EPA and availability tests. Leaching results have shown that lead and chromium are stabilized by prevailing chemical mechanisms and are always released in low amounts. On the other hand, cadmium is fixed by a prevailing physical mechanism. Despite this, cadmium release does not exceed about 10% of the initial quantity provided that the sample retains physical integrity. Finally, the system tuff-lime-gypsum has proven to offer better performance in respect to cement-based stabilization systems.

Keywords:

• Zeolitic tuff
• heavy metals
• ion exchange
• waste stabilization
• building materials