Environmental Science and Pollution Research
Table 1 Mineral co m position of fillers in different kinds of used paper (weight %) deter m ined by the X-ray diffraction m ethod
Mineral phase Che m ical for m ula
Office paper Journals
Cardboard Mixture
wt. %
Anhydrite
CaSO 4
0.40 ± 0.18
0.12 ± 0.04
C2Sα
Poly m orphic dicalciu m silicate (2CaO*SiO 2 )
0.63 ± 0.28 10.25 ± 3.57
0.33 ± 0.15
6.81 ± 3.23
1.09 ± 0.42
Portlandite
Ca(OH) 2
Li m e
CaO
2.56 ± 0.87 0.88 ± 0.36
0.24 ± 0.11
CaCO 3 –trigonal CaCO 3 –hexagonal
9.08 ± 2.55 11.30 ± 13.20 10.19 ± 3.56 6.88 ± 2.19
Calcite Vaterite
1.09 ± 0.22
3.40 ± 0.78
CaCO 3 –orthorho m bic 1.11 ± 0.38
Aragonite
Mg 3 Si 4 O 10 (OH) 2
0.05 ± 0.02 0.27 ± 0.14
Talk
Quartz
SiO 2
Ash
14.47 ± 2.87 29.05 ± 10.87 10.87 ± 2.26 11.70 ± 3.37
2016). Enhance m ents in ink adhesion and overall printing perfor m ance can be achieved through the incorporation of polyurethane-based poly m ers (Liu et al. 2022).
K 1 = [HCO −
2 − 3 ]][H
2 − 3 (aq)
− 3 (aq)
H +
+ ]
(aq) + CO
↔ HCO
3 ]∕[CO
(2)
− 3 (aq)
2 (aq) + H 2 O (l) K 2 = [CO 2 ]∕[HCO − 3 ][H + ]
H +
(aq) + HCO
↔ CO
(3)
Separation of cellulose fibres and their basic characterization
CO 2 (aq)
↔ CO
2 (g) K H =P(CO 2 )∕[CO 2 ]
(4)
The a m ount of calciu m (Ca) extracted depends on sev- eral factors, including solvent type and concentration, particle size, and the solid-to-liquid (S/L) ratio. For paper sludge, Ca concentration in solution increased up to pH 5.5, where m axi m u m leachability was observed, reaching 54% when using 0.7 M HCl or CH 3 COOH at an S/L ratio of 1:25 (Ki m and Ki m 2018). In the case of office paper leaching, hydrochloric acid (HCl) concentrations above 0.12 M caused the solution pH to drop below 5. Si m ilarly, when acetic acid was applied, pH fell below 5 at concentrations exceeding 0.2 M CH ၸ COOH. Acetic acid at 0.2 M de m onstrated higher effi- ciency in carbonate re m oval, as evidenced by ash reduc- tion and decreased Ca content in the e m bossed cellulose fibres (Fig. 2). At this concentration, Ca re m oval efficiency reached 95% and was further i m proved to 98.5% following subsequent washing. The re m oval of carbonates to isolate pure cellulose fibres in an acidic m ediu m is effective for office paper, cardboard, and m ixed paper, where carbonates represent the pri m ary filler co m ponent. The potential applications of separated cel- lulose are largely deter m ined by its physicoche m ical prop- erties, including crystallinity, purity, particle or fibre size, surface che m istry (presence of hydroxyl groups), ther m al stability relevant for co m posite m anufacturing, and its reac- tivity/ m odifiability enabling functionalization. The fibre di m ensions were influenced by the applied disintegration m ethod. The lengths ranged fro m 0.88 to 5.93 mm , with an average of 2.87 ± 1.38 mm . The widths
Waste paper cellulose is typically obtained through a co m - bination of che m ical and m echanical processes. The three m ost co mm only used m ethods include pre-hydrolysis (using either alkali or m ineral acid), alkaline pulping (typically with NaOH), and subsequent bleaching using hydrogen peroxide (H 2 O 2 ) or sodiu m hypochlorite (NaOCl) (Hanafiah et al. 2019; Gunjan et al. 2023). These conventional processes are technically de m anding; therefore, in our study, we opted for a si m pler approach: releasing cellulose fibres by dissolv- ing the filler m aterial, PCC. Precipitated calciu m carbonate, a synthetically produced filler co mm only present in waste paper, exhibits properties distinct fro m those of natural cal- cite. It contains all three poly m orphous m odifications of cal- ciu m carbonate: calcite + aragonite + vaterite. Recent studies highlight PCC’s higher purity, controlled m orphology, and surface m odifiability, m aking it m ore suitable for industrial processing and the effective release of cellulose fibres (Ki m et al. 2021). Given these differences, our research focused on identifying the m ost effective dissolution m ethod to release the e m bedded cellulose fibres. Mineralogical analysis of office paper (Table 1) confir m s that the filler consists exclusively of various crystalline for m s of calciu m carbonate (CaCO ၸ ), which are soluble in slightly acidic environ m ents. The dissolution of calciu m occurs according to the reactions described in Eqs. (1–4) Phipps and Lorusso (2001):
2 +
2 − 3 ]
2 − 3 (aq)
2 +
CaCO 3 (s)
↔ Ca
(aq) + CO
K so = [Ca
][CO
(1)
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