Rice Husk Ash to Stabilize Heavy Metals Contained in Municipal Solid Waste Incineration Fly Ash: First Results by Applying New Pre-treatment Technology

Abstract

A new technology was recently developed for municipal solid waste incineration (MSWI) fly ash stabilization, based on the employment of all waste and byproduct materials. In particular, the proposed method is based on the use of amorphous silica contained in rice husk ash (RHA), an agricultural byproduct material (COSMOS-RICE project). The obtained final inert can be applied in several applications to produce “green composites”. In this work, for the first time, a process for pre-treatment of rice husk, before its use in the stabilization of heavy metals, based on the employment of Instant Pressure Drop technology (DIC) was tested. The aim of this work is to verify the influence of the pre-treatment on the efficiency on heavy metals stabilization in the COSMOS-RICE technology. DIC technique is based on a thermomechanical effect induced by an abrupt transition from high steam pressure to a vacuum, to produce changes in the material. Two different DIC pre-treatments were selected and thermal annealing at different temperatures were performed on rice husk. The resulting RHAs were employed to obtain COSMOS-RICE samples, and the stabilization procedure was tested on the MSWI fly ash. In the frame of this work, some thermal treatments were also realized in O2-limiting conditions, to test the effect of charcoal obtained from RHA on the stabilization procedure. The results of this work show that the application of DIC technology into existing treatment cycles of some waste materials should be investigated in more details to offer the possibility to stabilize and reuse waste.

Review of the Reuse Possibilities Concerning Ash Residues from Thermal Process in a Medium-Sized Urban System in Northern Italy

“…Upon burning, cellulose and lignin are removed from RH, leaving behind silica ash. Indeed, the chemical composition of RHA has demonstrated that nearly 90% is composed by SiO 2 , and the other part by metal oxides, such as Al 2 O 3 , MgO, Fe 2 O 3 , CaO, Na 2 O, and K 2 O [24,[33][34][35][36][37][38]. The relevant amount of SiO 2 makes this kind of ash highly porous and lightweight, with a very high external surface area.…”

Beyond waste: new sustainable fillers from fly ashes stabilization, obtained by low cost raw materials

“…Because the cost of this process is high, being dependent on the colloidal silica quotation, recently the technology was improved by the substitution of commercial silica with rice husk ash (RHA), an agricultural by product of rice cultivation ( Benassi et al, 2015a ; Bosio et al, 2014a ). This project, named COSMOS-RICE, has already shown the capability to produce new fillers, by using stabilized waste ( Ponsot et al, 2015 ; Benassi et al, 2015b ; Bosio et al, 2014b ; Besco et al, 2014 ; Zacco et al, 2012 ; Besco et al, 2013 ), that were inserted in polypropylene, polyethylene, nylon, some resins and ceramics. It is possible to obtain attractive and sustainable products that can compete with the market of natural raw materials on the global stage.…”

Stabilization of Municipal Solid Waste Fly Ash, Obtained by Co-Combustion with Sewage Sludge, Mixed with Bottom Ash Derived by the Same Plant

“…MSWI-FA is generally considered the most problematic incineration waste, due to the presence of leachable heavy metals [3]. Several technologies for MSWI-FA stabilization have been already proposed [4][5][6][7][8] with the aim to promote its reuse [9][10][11]. Even though some recently proposed MSWI-FA treatments were defined as zero-waste technologies [12], they often require MSWI-FA pre-treatments, which need the use of some additional processes and raw materials.…”