Kolemanitten borik asit üretiminde mevcut teknolojideki temel sorun kolemanit cevheri içindeki yan minerallerin reaksiyon ortamında bozunmasıyla safsızlık sorunu yaratarak prosesten, verim düşüklüğüne neden olan çözelti deşarjı gerektirmesidir. Çalışmanın amacı, reaksiyonun sülfürik asit yanında propionik asit veya kalsiyum propionat katkılı ortamda gerçekleştirilerek proseste safsızlık kontrolünün mümkünlüğünü araştırmak, uygun proses koşullarını belirlemek ve yeni bir üretim prosesi geliştirmektir. Farklı proses alternatifleri değerlendirilerek proseste devreden bileşenin kalsiyum propionat olduğu yöntem seçilerek modellenmiştir. Kimyasal ve mineralojik yapıları belirlenmiş beş değişik tenörlü kolemanit cevherlerinin %10’luk propionik ve sülfürik asitlerle bozundurulmasıyla çözeltiye safsızlık geçişleri incelenmiş ve propionik asitli ortamda kil minerallerinin bozunmasının engellenebileceği belirlenmiştir. Değişik oranda propionik asit-sülfürik asit karışımları ve değişik tenörlü kolemanit cevherleri kullanılarak kesikli veya sürekli çalışan reaktörde reaksiyonun yürüyüşü ve çözeltiye geçen safsızlıklar izlenmiş ve reaksiyonda oluşan süspansiyonların filtrasyon hızları ölçülmüştür. Deneylerden, kalsiyum propionat varlığının çözeltiye geçen magnezyum ve silis konsantrasyonlarını önemli ölçüde azalttığı, sodyum ve potasyum geçişini ise hemen hemen engellendiği görülmüştür. Ortamdaki kalsiyum propionat oranı arttıkça, kalsiyum propionatın kil minerallerini dağıtması nedeni ile filtrasyon hızının düştüğü belirlenmiştir. Sonuç olarak, kolemanitten sülfürik asit yanında kalsiyum propionat kullanılmasına dayanan yeni borik asit üretim prosesinde çözeltiye safsızlık geçişi azaltılarak proses veriminin yükseltilebileceği gösterilmiştir. Anahtar Kelimeler: Borik asit, kolemanit, propionik asit, proses geliştirme, safsızlık kontrolü.The most important problem of the current boric acid production process from colemanite ore is the decomposition of side minerals in colemanite ore in the reaction media, which leads to impurity problems and causes some of the process liquor to be purged, therefore process efficiency decreases and environmental problems arise. The aim of this study is to investigate the possibility of impurity control in the process by performing the reaction in the presence of propionic acid or calcium propionate beside sulfuric acid, to determine the appropriate process conditions and to develop a new process that can be an alternative to the conventional one using solely sulfuric acid. Since intake of the impurities into the solution is sourced from the side minerals in the colemanite ore in the boric acid production process, it is necessary to determine the chemical and mineralogical structure of the colemanite ores and their interaction with acids. For this purpose, firstly, chemical and mineralogical structures of different colemanite ores were determined. Subsequently, the concentration of impurities captured by the solution in the presence of solely propionic acid by decomposing these ores with 10% propionic acid solutions, and, the amount, the chemical and mineralogical structure of the remaining solid obtained from these decompositions were determined. Concentrations of impurities transferred into the solution were determined by also decomposing these ores with 10% sulfuric acid solutions. By comparing the concentrations of sodium, potassium, magnesium and aluminum in solutions obtained by decomposing ores in propionic and sulfuric acid solutions, where these impurities do not precipitate, it was concluded that in the presence of propionic acid the decomposition of clay and feldspar minerals could be prevented. After assessing alternative models, the process model in which calcium propionate is the recycling component was selected and modeled. Batch and continuous reaction and filtration experiments were performed in accordance with this model. Advance of the reaction was followed by chemical analysis, transfer rates of the impurities into the solution were determined during batch reactions of different colemanite ores with different propionic acid-sulfuric acid mixtures and the filtration rates of the suspensions obtained from the reactions were measured under constant pressure difference. It was determined that the reactions could be performed in conformity with the model, provided that the concentration of calcium propionate is lower than 3% in the production liquor in order to prevent calcium borate precipitation. Impurity concentrations captured by 18% boric acid solution in reaction conditions were determined and considered as the unavoidable impurity concentrations. By taking these unavoidable concentrations into consideration, it was shown that the concentrations of magnesium and silica transferred into the solution could dramatically be decreased and the transfer of the sodium and potassium could practically be prevented in the presence of propionic acid. Based on the filtration rate measurements of reaction products, it was determined that the filtration rates were decreased by increasing concentrations of calcium propionate in the media and the cause of this decrease was the swelling and consequently the dispersion of the clay minerals in the presence of calcium propionate. It was investigated whether the reactions are performed in accordance with the model in the reac-tions of different colemanite ores with different sulfuric acid-propionic acid mixtures in the continuous reaction system. The impurity intake of the solutions obtained from the reactions was determined. Similar to the results obtained from batch reaction experiments, it was found out that the intake of magnesium, silica, sodium and potassium to the solution was decreased dramatically. From the measurements of first and second filtration rates under constant pressure difference, similar results were obtained to those obtained from batch experiments. In conclusion, it was shown that product quality and process efficiency could be increased and the environmental impact of the process could be decreased by decreasing the impurity intake of the solution in the new boric acid production process based on the reaction of colemanite ore with sulfuric acid in the presence of calcium propionate. Keywords: Boric acid, colemanite, propionic acid, process development, impurity control
