Millions tons of waste are discharged worldwide every day; most of it is dumped in landfills or discharged to rivers and seas without prior treatment. However, while the demand for waste disposal capacities is increasing, the availability of suitable sites is on the decline. Waste has become a critical problem for industrial society, particularly in big cities and densely areas. Therefore, the need to avoid or reduce the waste and to recycle it will become an over important political and economic issue. However, disposal capacities will continue to decrease in spite of the reduction in the volumes of waste produced. For this reason it is necessary to coordinate and optimize waste management. One of these options is incineration. Incinerator emissions can be generalized into the following four categories: (1) particulate emissions; (2) gaseous emissions, such as sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), and hydrochloric acid (HCl); (3) metals; and (4) miscellaneous gas emission. Emitted gases such as SO2, HCl, and NO2 contribute heavily to acid rain and smog, and to the photochemical formation of ozone in smog in sunlight. SO2, NO2, and ozone have been proven to cause respiratory illness, and smog has been shown to cause increased death rate .
Various technologies to remove SO2 in flue gas have been studied. Dry and wet processes are commonly used. Dry process is superior to the wet one in terms (1) inexpensive, (2) easy handling, and (3) no produces of liquid waste. One of processes in dry process category is bag filter reactor that uses Ca(OH)2 as absorbent. However, this process posses shortcomings, i.e. low sorbent conversion and low gas separation efficiency .
To enhance the efficiency of gas removal and the sorbent utilization, various additives have been examined. Sorbents obtained by mixing hydrated lime with different sources of silica have led to significantly higher conversion of calcium compared to the conversion obtained using pure hydrated lime . The use of diatomaceous earth (DE) as a silica source for absorbing acid gases has not been studied deeply. DE is a pozzolonic material and its main components are SiO2, Al2O3, and CaO . Figure 1 shows the model of pozzolanic reaction of Ca(OH)2 with silica-containing DE.
Gambar 1. Pozzolanic reaction model of Ca(OH)2 with DE 
SO2 absorption using sorbent of Ca(OH)2 in a bag filter reactor is about 60-70% . This level is likely to be enhanced by increasing the sorbent reactivity. One way to enhance the reactivity of the sorbent can be achieved by the addition of silica into the sorbent followed by calcination process. In this study, diatomaceous earth (DE) is used as a source of silica. The objective of this work is to test the activity of absorptive capacity of sorbent Ca(OH)2 by the addition of DE and to study the characteristics of the sorbent. Sorbent absorption capacity is tested by methylene blue analysis.
The hydrated lime...