As discussed earlier in this blog, a vitrified matrix or slag is the primary solid byproduct of plasma arc waste-to-energy processing. The vitrified matrix from plasma arc processing contains the mineral matter associated with the feed materials in a vitrified form – a hard, glassy-like substance. The amount of matrix produced is a function of how much non-combustible mineral matter is present in the feedstock.
This matrix is the result of operating temperatures within the plasma arc reactor above the melting temperature of the mineral matter. Under these conditions in the plasma arc reactor, non-volatile metals and metal oxides bind together in molten form until it is cooled via natural heat loss or via a pool of water, where it would fracture and granulate.
The compressive strength of a slag sample generated from fly ash from coal-fired power plant as well as some sodium carbonate (fluxing agent) was 480 kg/cm2, while its average mortar strength was tested at 169 kg/cm.
The vitrified matrix or slag generated by plasma arc treatment is primarily made up of silicon dioxide (SiO2), aluminum oxide (Al2O3) and calcium oxide (CaO). Toxicity Characteristic Leaching Procedure (TCLP) tests are designed to determine the mobility of both organic and inorganic analytes present in the slag. The most recent TCLP results on the vitrified matrix from the plasma arc waste-to-energy system located at a China refinery is presented in the below table.
||USA – EPA
(40 CFR 261.24)
|Arsenic||5||5||ND < 0.050|
|Cadmium||1||1||ND < 0.008|
|Chromium||5||5||ND < 0.017|
|Hexavalent Chromium||2.5||ND < 0.25|
|Lead||5||5||ND < 0.018|
|Mercury||0.2||0.2||ND < 0.0005|
|Selenium||1||1||ND < 0.041|
|Silver||5||5||ND < 0.013|
|ND = Not Detectable (detectable limit follows)
NR = Not reported