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Biooglje je produkt z velikim deležem aromatskega ogljika, ki nastane ob pirolizi biomase pri apoksičnih ali anoksičnih pogojih in relativno nizkih temperaturah. Na njegovi površini se nahajajo funkcionalne skupine s kisikom, ki doživijo deprotonacijo, in zato delujejo kot nosilec negativnega naboja. Od količine negativnih mest na biooglju je odvisna njegova kationska izmenjalna kapaciteta (KIK), ki izraža sposobnost materiala, da sprejme oziroma zadrži katione. KIK je v veliki meri odvisna od vrste vhodne biomase in temperature pirolize. Z naraščajočo temperaturo pirolize pride do odstranitve funkcionalnih skupin s kisikom, kar vodi v upad KIK. Vpliv biomase sem opazil tudi sam, saj so analizirani vzorci oglja, proizvedeni iz različnih vrst biomase, imeli zelo različne KIK. Vrste biooglja z visokimi KIK imajo pozitivne učinke na kvaliteto prsti. V prsti, ki je vsebovala biooglje, je bilo namreč opaženo boljše zadrževanje hranil, večja dostopnost zraka in vode, višja KIK prsti ter boljša adsorpcija težkih kovin. Biooglje je v prsti sposobno povečati tudi sekvestracijo CO2, ugodno pa vpliva še na rast nekaterih mikroorganizmov. Metod za določanje KIK organskih materialov je veliko. V diplomskem delu sem KIK biooglja določal po metodi z amonijevim acetatom (pri pH 7) in preko seštevanja izluženih baznih kationov (Na+, K+, Ca2+, Mg2+). Vzorcem sem najprej pH vrednost nastavil približno na 7, nato pa jih nasičil z NH4+ ioni. Ob tem je prišlo do izmenjave baznih kationov, ki sem jih z atomskimi spektroskopskimi metodami (AAS, AES) določil v izluženi raztopini. V zadnjem koraku sem NH4+ ione na biooglju izmenjal s K+ in jih določil s spektrofotometrom. Rezultate dobljene z omenjenima metodama sem nato primerjal in ugotovil, da je vsota baznih kationov precej večja od množine negativnega naboja na oglju, ki sem ga določil z NH4OAc. Pri primerjavi vrednosti KIK biooglja moramo torej upoštevati uporabljeno metodo. Biochar is a product with high content of aromatic carbon. It is produced when biomass is pyrolyzed at hypoxic or anoxic conditions and relatively low temperatures. On biochar's surface functional groups with oxygen are deprotonated and are therefore carrier of negative charge. The amount of said charge directly affects cation exchange capacity (CEC), which is used to express the ability of biochar to accept or retain cations. CEC values are very much affected by pyrolysis temperature and type of used biomass. With increasing pyrolysis temperature, the removal of functional groups with oxygen occurs, leading to a decrease in CEC. The effect of biomass can be observed in the experimental part of my diploma thesis, as the analysed biochar samples produced from different types of biomass had very different CEC. Biochar types with high CEC values have positive impact on soil quality. In soils, containing biochar, better nutrient retention, air and water availability, higher CEC and better adsorption of heavy metals was observed. Biochar in soil is also able to enhance CO2 sequestration and growth of some microorganisms. There are many different methods for determination of CEC in organic compounds. In diploma thesis I determined CEC of biochar with two methods: with ammonium acetate (at pH 7) and by summation of base cations (Na+, K+, Ca2+, Mg2+). Firstly, I adjusted the pH value of samples to about 7 and then saturated them with NH4+ ions. This caused the exchange of base cations, which I determined in leached solution by atomic spectroscopic methods (AAS, AES). In the last step I exchanged NH4+ ions absorbed on biochar with K+ ions and determined them with spectrophotometer. I then compared the results obtained with these two methods and found that the sum of base cations is substantially larger than the amount of negative charge on biochar determined with NH4OAc. When comparing CEC values of biochar, we must therefore consider the method used. |
