Alkali salt recovered from kraft process and its application as dyeing auxiliary

Recovered Boiler Ash (RBA) collected from kraft pulping process was purified using crystallization and evaporization methods. The study parameters were crystallization time (24, 48, 72 and 96 h), crystallization temperature (−5 °C and 5 °C), evaporation temperature (50 °C, 80 °C and 100 °C) and stirring effect. Results demonstrated that the maximum yield of crystallized compounds (CRBA) reached 68 ± 3 wt.% when the crystallization was conducted at 5 °C for 48 h at pH 3 with no stirring, while that of evaporated compounds (ERBA) reached 95 ± 4 wt.% when the evaporation was conducted at 100 °C and pH 3 under stirring. The components found in RBA and all recovered salts were examined by inductively coupled plasma (ICP) spectrophotometry and ion chromatography (IC). It was found that RBA consisted of 80 wt.% Na2SO4, 5 wt.% NaCl and 1 wt.% Na2CO3. After purification, CRBA and ERBA showed weight ratios of Na2SO4:NaCl:K2SO4 as 96.4:0.8:2.8 and 78.3:11.1:10.6, respectively. These results were in agreement with data from their X-ray diffractograms (XRD), differential scanning calorimetry (DSC) and specific densities. Due to the reasons of yield and cost saving, ERBA was utilized as an auxiliary for silk fabric dyeing. The dyeing was carried out using three commercial reactive dyes specially for silk dyeing: Cibacron® Red FN-R, Cibacron® Blue FN-R, Cibacron® Yellow FN-R. RBA and ERBA were used as auxiliaries at the concentrations of 30–60 g L−1. The dyeing performances indicated that the best dyeing result was shown when 45 g L−1 ERBA was used as auxiliary for silk fabric dyeing.