Changes in phlogopite mineralogy during the process of enriched compost production

Soil is the thin layer of materials covering the Earth’s surface and forms from the interaction of the atmosphere, lithosphere, biosphere and hydrosphere. Soil formation, development and functions influence the sustainability of ecosystem. The unique characteristics of soil have made it one of the key subjects of the Earth Science. Minerals are important components of the soil environment. They influence on the water-holding capacity of soils and affect their cation exchange capacity. Mineral weathering is an important process in soils, during which available forms of important nutrient elements are released from minerals structure into the soil system for root uptake. Micaceous minerals are common components of soils, sediments and minerals. Several studies have examined the characteristics of compost enriched with mineral compounds. While the mineralogical changes during the process of compost production have not yet been investigated. Therefore, the objective of this research was to evaluate the rate of biological weathering of phlogopite with time in phlogopite-enriched compost.

An experiment was run in petri dishes under laboratory conditions using 2 levels of phlogopite mineral (0 and 20% by weight) and four time periods (45, 90, 135 and 180 days) in 3 replications. Each petri dish contained 20 g of a mixture of cow manure and phlogopite mineral. In each period, 6 petri dishes were separated and their contents were oven dried at 30 °C, powdered and passed through a 2 mm sieve. After preparing the contents of petri dishes, organic carbon content of the samples was measured by wet oxidation method and their total nitrogen by Kjeldahl method. The mineralogical changes were evaluated using X-ray diffraction analysis.

XRD patterns showed that during the composting process, phlogopite was partially weathered to vermiculite and smectite. The rate of weathering was higher at the early stages. The weathering of phlogopite was influenced considerably by the activity of microbial communities during organic matter decomposition process. At the end of the composting process, the weathering rate decreased and continued at a stable rate. Mineralogical changes occurred in phologopite during the composting were in line with the reduction of C/N ratio with time. The C/N ratio rapidly changes at the early stages of the composting process and gradually becomes constant.

In general, the results indicate that the increase of availability of elements such as potassium in mica-enriched compost is in fact due to the weathering of micaceous minerals added. The weathering rate was influenced by the activities of microbial communities.