Wood ash is the organic and inorganic residue remaining after combustion of wood. When ash is produced in industrial combustion systems, the temperature of combustion, cleanliness of the fuel wood, the collection location, and the process have profound effects on the nature of ash material. The wood ash is used mainly to produce potash for fertilizer and alkali for industry. Wood ash is a good source of many micronutrients needed in trace amounts for adequate plant growth. Calcium is the most abundant element in wood ash and gives ash properties similar to agricultural lime. In this experiment, the influence of burning temperature on ash production from non-volatile combustible wood bark of mango tree has been evaluated.
Approximately 10 g of dry wood bark of mango tree was placed in a ceramic dish and burnt in a muffle furnace. In the first phase burning of wood bark was carried out at 500 °C to obtain a low temperature ash. For chemical analysis, samples were obtained by heating the ash at temperatures of 600 °C, 700 °C, 800 °C and 950 °C for over an hour and the concentration of inorganic elements, i.e. calcium, magnesium, potassium, iron, zinc, manganese in the ash was determined using Inductively Coupled Plasma Optical Emission spectrometer (ICP-OES) [Perkin Elmer Optima 7000 DV].
Results and Discussion
The concentration of inorganic elements in wood ash is listed in the following table.
Graphical representation is shown in Fig. 1, Fig. 2 and Fig.3
Influence of the burning temperature in the composition of wood ash was reflected in the concentration of each element in ash. Based on the experimental data, it follows that with increase in temperature the concentration of calcium increases markedly while that of potassium decreases, other elements showing a nearly constant concentration. The increase in calcium concentration is mainly due to the decomposition of its carbonate while a decrease in concentration of potassium is attributed to the decomposition of its carbonate and subsequent volatilization of its oxide.
Depending on the burning temperature of the non-volatile combustible matter, concentrations of calcium, magnesium, manganese, iron, zinc increased. However, the concentration of potassium decreased, which was attributed to the partial evaporation of this element as oxide during the thermal decomposition of mineral substances. The decrease in the concentration of potassium in ash from wood bark with increase in the burning temperature of non-volatile matter had a positive influence upon the thermal characteristics of the ash and the creation of ash in the form of loose matter.
Contributed by: Priya Das and Sukhenjit Datta under the guidance of Prof. B.K. Gupta