Surface adsorption of stearic acid by natural calcite

In order to obtain hydrophobic material, the surface of natural limestone with the high content of calcite (>95%), was treated with 0.5, 1, 1.5, 2, 3 and 4% of stearic acid. Two methods were used for modification: the solution method and the dry coating. The obtained products were characterized using the thermal analysis (DT/TG), X-ray powder diffraction analysis (XRPD), scanning electron microscopy (SEM) and by the evaluation of floating test. Results of floating test showed that when the solution method was applied, the hydrophobicity arrived at above 99% when the amount of stearic acid was 1.5%, while with the dry coating the same hydrophobicity was achieved with 3% of stearic acid. From the position of the principal exothermic peak (> 310 ?C) at DTA curves, for calcites modified with dry coating and with the solution method, it can be concluded that with both modification processes, the same active sites exist at the calcite surface onto which stearic acid may be chemisorbed. However, the position and the intensity of the other exothermic peaks, indicate the differences in bonding of stearic acid at the calcite surface during the solution method and the dry coating. U radu su prikazani rezultati modifikovanja povrsine kalcita suvim i mokrim postupkom. Kalcit je glavni i najzastupljeniji mineral kod prirodnog krecnjaka (>95%). Ispitivanja su vrsena na seriji uzoraka sa sadrzajem stearinske kiseline , kao povrsinski aktivne materije, od 0,5, 1, 1.5, 2, 3 i 4%. Na proizvodima dobijenim suvim i mokrim postupkom modifikovanja uradjena je diferencijalno termijska analiza (DTA), termo- gravimetrijska analiza (TG) i skenirajuca elektronska mikroskopija (SEM). Stepen hidrofobnosti uzoraka pracen je odredjivanjem indeksa oblozenosti. Rezultati pokazuju da je kod mokrog postupka najveci indeks oblozenosti od 99,9% dobijen je na uzorku sa sadrzajem stearinske kiseline od 1,5%, a kod suvog postupka kod uzorka sa sadrzajem stearinske kiseline od 3%. Rezultati termicke analize pokazuju da se osnovni egzotermni maksimum kod oba postupka javlja na priblizno istim temperaturama (>310 ?C) sto ukazuje na postojanje istih aktivnih mesta na povrsini kalcita na kojima moze biti hemisorbovana stearinska kiselina. Polozaj i intenzitet ostalih egzotermnih pikova ukazuje na razlicito vezivanje stearinske kiseline za povrsinu kalcita kod mokrog i suvog postupka.