D1 Stage Research Articles

Benefactor facilitation and beneficiary feedback effects drive shrub‐dominated community succession in a semi‐arid dune ecosystem

AbstractQuestions(a) How do the facilitative effects of benefactors on understorey species change along a successional gradient; (b) what are the feedback effects of the beneficiary species on the benefactor; and (c) how do these bidirectional interactions drive community dynamics of a shrub‐dominated ecosystem.LocationA sand‐fixing community, Mu Us Desert, China.MethodsWe quantified the effects of the shrub Artemisia ordosica on understorey herb abundance, biomass and richness using an observational procedure at four positions along a successional gradient, i.e., semi‐fixed dunes (D1 stage), fixed dunes (D2 stage), fixed dunes covered with biological crusts (D3 stage) and fixed dunes with herbs (D4 stage). The relative interaction index (RII) was used to calculate the effect of the shrub on the herbs. Additionally, we conducted a removal experiment at the latest successional stage to assess the beneficiary feedback effects on the growth of the shrub's vegetative and reproductive twigs.ResultsThe response of herbs to the effect of the benefactor shrub showed a humped‐back curve for abundance and biomass along the successional gradient, supporting the collapse of the interaction model, but a linear curve for richness, thus supporting the stress‐gradient hypothesis. This difference could likely be explained by a turnover of life‐history groups of understorey species from annuals to perennials along the successional gradient, with the growth of the latter group being more susceptible to shrub facilitation than the former. The herbs had a negative feedback effect on the growth of the shrub's reproductive twigs.ConclusionsOur results suggest that the relationship between the shrub A. ordosica and the associated herbs was antagonistic, and the absence of shrub seedling recruitment at the end of succession suggests that this antagonistic relationship was a crucial driver of a successional shift from a shrub‐dominated to a herb‐dominated community.

Permian pyroxenite dykes in harzburgite with signatures of the mantle, subduction channel and accretionary wedge evolution (Austroalpine Unit, Eastern Alps)

Websterite and garnet orthopyroxenite and clinopyroxenite dykes crosscutting harzburgite occur in the hanging wall of a Cretaceous eclogitized continental fragment of the Upper Austroalpine Unit in the Eastern Alps. The dyke textures reflect pressure–temperature changes from the mantle, subduction channel and an accretionary wedge. A clinopyroxenite dyke, dated at 252 ± 2 Ma on zircon by UPb SIMS, provided εHf(t) zircon values of 16–8 (av. 11 from 18 spots) suggesting a depleted mantle source. The rock modal mineral composition and the mineral and whole-rock chemistry revealed that the pyroxenite dykes' petrogenesis is most likely related to sub-crustal cumulate-type melt derivates, less evolved for websterites and highly evolved for clino- and orthopyroxenites. The porphyroclastic clinopyroxene1 (10–13 mol% Ca-Ts), orthopyroxene1, spinel1 and amphibole1 are inferred remnants after magmatic phases. They contain Ti-spinel and ilmenite exsolutions which indicate cooling of the dykes in harzburgite in a Spl stability field (D0-1 stage). Garnet exsolutions in Cpx1, Opx1 and Amp1, and Cpx exsolutions in Amp1 document continuous cooling and/or pressure increase (D0-2 stage). The Grt coronas around Spl1, Opx1, Cpx1 and Amp1, and the granoblastic matrix of Prp–Grs-rich Grt (or Cr-Spl in websterites), low-Al Cpx, low-Al Opx, Fe-enriched olivine, zoisite, kyanite, rutile and pargasite record a subduction channel compression (D1 stage). While the formation of Cpx–Grt or Amp-Grt symplectites replacing the Cpx1 and Amp1 rims suggests the HP–HT decompression (D2-1 exhumation stage). The Grt (or Cr-Spl) replacement by Spl, and Opx1, Cpx1 and Prg replacement by Ol–Spl, Opx–Spl or Prg–Spl symplectites document continuous HT decompression (D2-2 exhumation stage). The MP/MT–LT conditions were estimated from tremolite, Grs-rich Grt, Sr-epidote, clinozoisite, Cl-apatite, titanite, Ce-allanite, chlorite, serpentine and talc assemblage (D3 stage). Anticlockwise P–T path was reconstructed for the D0 to D1 stages followed by almost isothermal exhumation (D2) and emplacement in the Cretaceous accretionary wedge (D3). The pseudosection P–T calculation from a clinopyroxenite dyke yielded 850–825 °C and 25–28 kbar (D1). The whole-rock and mineral trace element data of relic Cpx1 and Amp1, Grt(1–3), Ep–Zo, and younger zircon ages due to Pb-loss, reflect the impact of metamorphic fluids during the D1 to D3 evolutionary stages.

The structural deformation characteristics and the control of gold mineralization of the upper Triassic flysch (Langjiexue Group) in Tibetan Plateau

Located in the eastern section of the Indus‐Yarlung Tsangbo Suture Zone, the Triassic Langjiexue Group is also very important for the distribution of the orogenic gold deposits, such as Bangbu and Zhemulang. Two regional profiles (Jiacha profile and Lang County profile) in the Langjiexue Group have been chosen for systematic mapping. Combing with the method of Ar–Ar dating for mica, this paper provides a detailed analysis of the structural movements and stress periods of the Langjiexue Group, and the relationship between them with the orogenic gold deposits distributed within it, and finally, establish the structural control model for orogenic gold deposits in the Langjiexue Group. The structural deformation of the Langjiexue Group can be divided into 4 stages. In the D1 stage, shallow ductile shear played a dominant role with the principal stress of the reaction in a nearly E–W direction. The main stress of D2 stage was in an obviously S–N direction whose foliation of the axial surface was a ubiquitous phyllitic foliation and foliation. The structures of the D3 stage were superimposed on those of the D2 stage with the main stress of S–N direction. In the D4 stage, the principal stress of the structural movements was in a nearly E–W direction. According to the morphology and spatial positions of the profile folds, the main body of the Songre Formation in the southern parts of the tectonic profiles can be restored into a large reverse antiform, whereas the main body of the Tectonic mélange zone in the northern parts can be restored into a continuous large antiform and synform. Judging by the Ar–Ar plateau ages (56.04 ± 0.72 Ma, 47.98 ± 0.46 Ma) of the sericite in the two quartz veins that were arranged along the axial plane cleavage of the folders in D3 stage, the widely distributed quartz veins in the Langjiexue Group were mainly the outcome of fluid action accompanied by the structural deformation that occurred in the main Indo‐Asian collision orogenesis period, which were in consistent with the mineralogenetic epoch of the orogenic gold deposits in this region.

Structural controls on the Lala iron-copper deposit of the Kangdian metallogenic province, southwestern China: Tectonic and metallogenic implications

The Lala Fe-Cu deposit is a typical iron-oxide copper-gold (IOCG) deposit of the Kangdian region, southwestern China. Structural controls on the orebodies are suggested but not well-understood. Herein, structural analysis is conducted in the Luodang open-pit of the Lala deposit. It reveals that the Lala deposit has undergone multiple deformation events. The D1 stage is the earliest and corresponds to a late Paleoproterozoic rifting, resulting in the Hekou Group (host rock) deposition and the development of bedding-parallel foliation. The D2 event is syn-mineralization and coincident with an ESE-trending compression. During the D2 compression, the bedding-parallel foliations were preferentially dilated and facilitated ore-forming fluid infiltration, ore replacement and the infilling of bedding-parallel veins. As the compression continues, folding via flexural-slip has enhanced the bedding-parallel veining and, moreover, has induced further dilation along the fold hinges, where “saddle-reef” type ore shoots have been developed. The D3 event represents an ESE-directed extension, which has induced an overprint of the mineralization, characterized by biotite-sulfide veins crosscutting the stratiform ores at high angle. The E-W trending structures, faults and folds probably represent a post-mineralization north-south compression (D4). In combination with previous paragenetic and geochronological studies, the D2 and D3 mineralization is inferred to occur at ca. 1.05 Ga and ca. 0.83 Ga respectively. The timing and corresponding stress regimes of the deformation events are more consistent with a tectonic model that suggests the late-Mesoproterozoic to early Neoproterozoic (1.05 Ga–0.85 Ga) Yangtze block is in the process of amalgamation with the Cathaysia and in favor of horizontal compression, whereas the post-0.85 Ga Yangtze is dominated by rifting and extensional stress regime, with possible links to the Rodinia breakup. Structural interpretation of the Lala deposit demonstrates that (1) bedding-parallel shearing, (2) transitional ductile-brittle condition and (3) mildly elevated fluid pressure are the essential factors corresponding to the development of strata-bound replacement-style IOCG mineralization and carries implications for other comparable IOCG deposits.

Emplacement of silica veins at a brittle shear zone in the Ahar region, NW Iran: Insights from structural analysis, analogue and numerical modeling

Post Eocene silica vein emplacement at a brittle shear zone in NW Iran is associated with Au, Cu and Mo mineralization. The orientation and abundance of veins are dominantly controlled by the fault and fracture pattern. Within this context, we have analyze the spatial and geometrical properties of the faults and fractures affecting vein emplacement and compare the results with analogue and numerical models to distinguish the proper area for the emplacement of ore bearing silica veins in the evolution of a brittle shear zone. For this purpose regional lineament trends have been extracted from Aster satellite image. The trends of this lineament are between N80°W to N60°W. Field observations revealed two dominant fracture sets with strike of N40°E and N20°W; as well as the silica veins general trend is N15°W. The brittle shear zone analogue model indicated that the first structure to appear in the D1 stage of deformation were the shear fracture. With the progress of deformation in D2 stage, shear fractures eventually grew, rotated and were connected to each other, which created surface ruptures in the models. The main surface rupture displays a misalignment with the basement shear zone. In the D3 stage, fractures rotated with increasing displacement along the strike slip faults. The numerical stress analysis model shows that in the D1 stage, compressive stress is localized in the central part of the shear zone, and the rupture developed. In D2 stage, stress in the central part significantly decreased from 0.14 to 0.09 MPa (67% of maximum value) and an extensional regime was dominant. In the D3 stage, the tips of the model were primarily influenced by extensional stress, whereas the central part was subdivided into two zones: one is high stress and compressive and the other is low stress and extensional. Shearing along strike slip faults led to subsequent deformation in D4. Our modeling data indicate that heterogenous stress distribution along the shear zone instigated the frequent inversion of the extensional basins to compressional and vice versa. The D2 stage of evolution of the shear zone was favorable time for the emplacement of ore bearing veins, because of open fractures and the prevailing extensional regime in the central part. Thus the young shear zone open fractures of the central part and the mature shear zone tension fractures in the tips are appropriate areas for emplacement of veins.

Superimposed deformation of the Solonker Belt and nearby regions in western Inner Mongolia, China

AbstractThe deformation of the Solonker Belt and nearby regions is helpful for understanding the tectonic evolution of the Central Asian Orogenic Belt. This study carried out structural analysis in the Mandula and Ganqi areas of western Inner Mongolia, including the Solonker Belt, the Southern Orogenic Belt and the northern Yinshan Belt (Langshan range). Our results reveal that the Solonker Belt, the Southern Orogenic Belt and the northern Yinshan Belt underwent two stages (D1 and D2) of deformation during the Mesozoic period. The D1 stage produced the NNE-directed thrusts and asymmetric folds, indicating a NNE–SSW contraction. The northern Yinshan Belt, the Southern Orogenic Belt and the Solonker Belt formed as a series of NNE-verging tectonic nappes. The D2 stage developed the NE-trending folds and the SE- or NW-directed thrusts that cross-cut the D1 structures. The two events of nearly orthogonal or oblique shortening gave rise to the superimposed structures (e.g. fold interference patterns). The quartz veins that filled the fractures of the D1 deformation contain zircons of Middle Triassic U–Pb ages. The new dating data, along with the regional sedimentary hiatus, led us to infer that the D1 stage of deformation occurred in Middle Triassic time and the D2 stage occurred in Late Jurassic time. We consider that the D1 stage of deformation resulted from a convergent event, which might be related to the closure of the Palaeo-Asian Ocean or limited, narrow ocean basins; and the D2 stage of deformation was the far-field result of subduction of the Palaeo-Pacific Ocean and the closure of the Mongol-Okhotsk Ocean.

Effect of hot chlorine dioxide delignification on AOX in bagasse pulp wastewater

This work describes the effect of the hot chlorine dioxide delignification (DHT) on the properties of bagasse fiber and the formation of AOX. The bagasse pulp was subjected to both DHT and normal temperature chlorine dioxide delignification (D0), and the AOX contents in the effluent were determined respectively. The GC–MS results showed that the main components of the D0 stage wastewater were chlorinated hydrocarbons and chlorinated diphenyls. In contrast, those AOXs in the DHT stage wastewater were very few. The GC–MS, ATR-FTIR, and XPS results showed the DHT process is more effective in the removal of the residual phenolic lignin and the hemicellulose-linked HexA compared with D0. Furthermore, in comparison, the AOX content could be reduced by 50% with DHT. The fully bleached pulp obtained via DHTEpD process has a higher brightness than that obtained by D0EpD, which provides a reliable theoretical basis for industrial application.

Osmoregulatory capacity, health status and growth as functions of moult stages from various weight classes in marron (Cherax cainii) and yabbies (Cherax destructor)

The study investigated the relationship between five moult stages and the osmoregulatory capacities (OC), moisture content of hepatopancreas (HM%), hepatosomatic indices (HIwet, HIdry) and growth of 6 weight classes of 235 marron (Cherax cainii) and 235 yabbies (Cherax destructor) under laboratory conditions. In each moult stage, OC increased linearly with the increase in wet body weight. Intermoult stage C showed the highest OC significantly lower than premoult stages D0, D1, D2 and postmoult stage AB in every weight class in both crayfish. HM% decreased from AB to D2, while both HIwet and HIdry reduced from C to D2. Percentage dry matter of whole body carcass was highest in stage C and lowest during the AB stage with a significant difference between the two species. Larger than 15-g marron and yabbies differ with each other in OC, HIwet, and HIdry, moult intervals and growth rates.

Bleaching optimization at WestRock mill in Covington, Virginia

The WestRock mill in Covington, VA, USA, initiated a long term diagnostic and optimization program for all three of its bleaching lines. Benchmarking studies were used to help identify optimization opportunities. Capital expenditures for mixing improvement, filtrate changes, equipment repair, other equipment changes, and species changes were outside the scope of this work. This focus of this paper is the B line, producing southern hardwood pulp in a D(EP)DD sequence at 88% GE brightness. The benchmarking study and optimization work identified the following opportunities for improved performance: nonoptimal addition of caustic and hydrogen peroxide to the (EP) stage, carryover of D0 filtrate to the (EP) stage, and carryover of (EP) filtrate to the D1 stage. As a result of actions the mill undertook to address these opportunities, D0 kappa factor decreased about 5%, sodium hydroxide consumption in the (EP) stage decreased about 35%, chlorine dioxide consumption in the D1 stage decreased about 25%, and overall bleaching cost decreased about 15%.

Kinetics of Adsorbable Organic Halogen Formation During the First Chlorine Dioxide Bleaching Stage of Eucalyptus Kraft Pulp

The emission standard for adsorbable organic halogen (AOX) has been adjusted as a mandatory assessment indicator in the papermaking industrial pollutants emission standards of China. To provide a theoretical basis to reduce AOX formation, a kinetic model of the first chlorine dioxide bleaching stage (D0) is presented for elemental chlorine-free (ECF) bleaching of eucalyptus kraft pulp. The kinetics of the D0 stage can be expressed as dW/dt = 314.6e-20.53/RT[H+]0.21[ClO2]0.41K0.98, where the reaction series for lignin, chlorine dioxide dosage, and H+ concentration are 0.98, 0.41, and 0.21, respectively. The reaction activation energy was 20.53 kJ.mol-1. R2 was greater than 0.9, which means that the model was shown to have high prognostic ability and feasibility. In the D0 stage, mostly lignin was removed and the reaction was fast. Much AOX was formed at the beginning of bleaching, and the reaction rate was primarily determined by the lignin content and chlorine dioxide dosage. H+ existed primarily as a catalyst and had little influence on AOX formation. The AOX formation occurs easily, as the reaction activation energy is less than 30 kJ.mol-1.

Dynamics of glucose in the haemolymph of female giant freshwater prawn,Macrobrachium rosenbergii,influences reproductive and non-reproductive moulting cycles

Glucose, when measured in haemolymph, has been found to reflect a useful predictor of energetic investment. This study evaluated the pattern of glucose in the haemolymph, with an attempt to gain a better insight into the role of glucose as nutritional source of ovarian development and energy reserves during reproductive and non-reproductive moulting cycles. The haemolymph of female giant freshwater prawn, Macrobrachium rosenbergii, was obtained at eight different moulting stages, and levels of glucose were determined using an enzymatic colorimetric glucose-oxidase method in parallel with a histological examination of ovarian development. Glucose levels were relatively low (0.15 ± 0.02 mg mL−1) at D0 stage, an abrupt increase (0.52 ± 0.13 mg mL−1) during premoult D1 stage and declined (0.32 ± 0.10 and 0.31 ± 0.09 mg mL−1) during premoult D2 and D3 stages, respectively; thereafter, a slight increase (0.43 ± 0.09 mg mL−1) occurred at post-moult A stage. The progression of ovarian growth, marked by an increasing gonadosomatic index (GSI) pattern during the reproductive moulting cycle (C0–D3 stages), was directly proportionate to fluctuations in glucose levels. GSI was significantly positively correlated with glucose (R = 0.40; P < 0.05). In contrast, glucose was notably higher at post-moult A and premoult D2 stages during non-reproductive moulting cycle, the period during which glucose is crucial for exoskeletal chitin synthesis. At this particular stage, a negative correlation between body weight and glucose (R = −0.36; P < 0.05) was observed. The dynamics of glucose in the haemolymph of female M. rosenbergii correlated with ovarian growth, which signify that glucose as nutritional source for vitellogenesis, and affects the body weight of this species.

Effects of D0-stage temperature, pH, and kappa factor on chlorine dioxide decomposition and D0-(EP)-D1 bleaching performance for eucalypt pulps

Mills have largely used chlorine dioxide (ClO2) for eucalyptus kraft pulp bleaching. Different mills have observed significant variation in ClO2 demand to reach full brightness (≥90 ISO). These large differences in ClO2 consumption derive from many factors. The most significant include differences in carryover loads and hexenuronic acid (HexA) contents and the level of chlorate formation across bleaching. Handling of pulp with high HexA content and ClO2 losses to chlorate can be minimized by proper operation of the ClO2 stages across the bleach plant. An oxygen delignified eucalyptus kraft pulp with a kappa of 10-12 units contains only 4-6 units actually derived from lignin. This scarce amount of lignin (0.6%-0.9%) is not able to consume high ClO2 doses and, as a consequence, the excess ClO2 applied can end up being converted into chlorate. Hence, proper optimization of ClO2 bleaching stages can save significant amounts of this oxidant. This study focused on optimizing ClO2 bleaching for a typical oxygen delignified eucalyptus kraft pulp of kappa number 11.7. Elemental chlorine free bleaching was carried out with the D0-(EP)-D1 sequence. The following conditions were varied in the D0 stage: temperature, end pH, and kappa factor. The results indicated that maximum ClO2 bleaching efficiency is achieved when minimum chlorate is formed, especially when ClO2 bleaching is adjusted in such a way that residual active chlorine is maintained to a minimum. The most significant variable affecting chlorate formation is pH; however, ClO2 doses (ClO2 concentration) also play a very important role. Chlorate formation is more intense in the D1 stage in relation to the D0 stage. Optimum conditions to run the D0 stage were 90°C, 3.5 pH, and 0.22 kappa factor.

Impact of dissolved lignin in oxygen delignification and chlorine dioxide stages

While carryover of dissolved lignin between stages in the pulp mill fiber line is a well-known problem, it is still typically seen only as a minor disturbance factor or bias in the control of oxygen (O2) delignification and bleaching stages. The present study, however, reveals that it plays a larger role than anticipated, and that it should be properly analyzed in order to correctly control the process stages. This is especially important for the O2 and D0 stages as the lignin content is still high in these positions. The results of the study show that dissolved lignin carried over between stages may have a significant impact on the bleaching chemical consumption and, indirectly, on the pulp quality. Mill investigations have shown very large variations in the dissolved lignin content in the pulp before the oxygen delignification stage and before the D0 stage that have significantly influenced the bleaching chemical demand and, subsequently, the degree of delignification. In order to develop a better understanding of the mechanisms of the dissolved lignin’s reactions, laboratory O2 and D0 experiments with controlled levels of dissolved lignin were conducted. It was anticipated that a better feedforward control could be achieved using an online dissolved lignin measurement, and results from mill trials are presented. Chlorine dioxide laboratory experiments using different levels of carryover (i.e., different dissolved lignin contents) were conducted. It was concluded that the filtrate kappa number provides a relevant measure of the bleach demand due to the dissolved lignin and that, subsequently, the combined fiber and filtrate kappa number provides an appropriate measure for optimum feedforward control of the stages. Mill results support these findings, which show that the chemical consumption is reduced significantly using the total kappa number. The post-D or post-DE kappa number feedback control can most probably be eliminated by using this technology.

Revised steady-state model for chlorine dioxide brightening that considers extraction washer carryover effects

In an earlier investigation, a generalized model was developed to simulate the first chlorine dioxide (ClO2) brightening stage (D1). That stoichiometric model accurately predicts pulp brightness values for given bleach charges and vice versa for laboratory softwood pulps. The equation parameters are dependent on the kappa number and brightness of the extracted pulp. In this study, the earlier model was refined to include the negative effects of extraction carryover to simulate more realistically a mill’s D1 stage. Extracted pulps that contain washer carryover were found to brighten as if the pulp had a kappa number equal to the sum of the extracted kappa and the kappa value of extraction dissolved solids. If this higher kappa (i.e., apparent or wet kappa) is used in place of the extracted kappa with the D1 model, the equations suitably predicted the bleached brightness for a given bleach charge. The modified expressions were used to quantify the amount of carryover and to calculate carryover bleach consumption for a softwood D0(EOP)D1 fiber line. The mill’s washed pulps were found to have carryover levels of 1.4 kappa units, which was consuming 48% of the total D1 bleach charge. Additional analyses revealed that extraction carryover consumes 2.5-4.6 kg ClO2/ton pulp per kappa unit of carryover when bleaching a pulp to 78% to 84% ISO.

Tectono-metamorphic evolution of the pre-Athabasca basement within the Wollaston–Mudjatik Transition Zone, Saskatchewan

The Paleoproterozoic tectono-metamorphic evolution of the pre-Athabasca basement (∼1.7 Ga) within the Wollaston–Mudjatik Transition Zone (WMTZ) (Saskatchewan, Canada) has been characterized using both exposed basement and drill cores from the Wolly–McClean exploration drilling project. The finite ductile strain pattern of the WMTZ results from the superposition of two tectono-metamorphic events M1–D1 and M2–D2. M1–D1 is associated with the development of a gently dipping foliation striking N90°–N100° and a southward decrease in peak pressures from up to 10 kbar (1 kbar = 100 MPa) in the Cochrane River area down to 6 kbar in the Wolly–McClean exploration drilling project. The M2–D2 event is responsible for the main northeasterly trend of the WMTZ that developed in a sinistral transpressional tectonic regime during the final oblique collision of the Trans-Hudson Orogeny. Thermobarometric estimations on M2–D2 assemblages show that the studied area was reequilibrated at about 4–5 kbar and 750–825 °C. The basement has thus been affected by a differential isothermal decompression event between D1 and D2 that allowed the juxtaposition of the deepest northeastern domains and the Wolly–McClean exploration drilling project, at the same structural level. These results suggest that the basement exposed to the northeast of the Athabasca Basin is not an analog of the basement located beneath the eastern Athabasca Basin where uranium-enriched granitic pegmatites and granites are known. We also suggest that uranium-enriched melts produced during the early M1–D1 stage of partial melting in the deep crust were transferred to the midcrust, owing to D2 shear zones, where they have differentiated to produce uranium-bearing pegmatites.

Xylanase-Aided Chlorine Dioxide Bleaching of Bagasse Pulp to Reduce AOX Formation

Xylanase pretreatment was used to improve the chlorine dioxide bleaching of bagasse pulp. The pulp was pretreated with xylanase, which was followed by a chlorine dioxide bleaching stage. The HexA content of the pulp and the AOX content of the bleaching effluent were measured using UV-Vis and GC-MS methods, respectively. The results showed that a good correlation occurred between HexA and kappa number. HexA content of the pulp decreased significantly after the xylanase pretreatment. The AOX content of the bleaching effluent decreased as HexA was removed from the pulp. It was found that AOX could be reduced by up to 29.8%, comparing XD0 with a D0 stage. Fourier transform infrared spectroscopy (FTIR) was employed to determine the breakage of chemical bonds in the pulp. It revealed that some lignin and hemicellulose were removed after xylanase treatment. The GC-MS results showed that some toxic chloride such as 2,4,6-trichlorophenol could be completely removed after xylanase pretreatment.

Effects of Additives on Absorbable Organic Halide Reduction in Elemental Chlorine-Free Bleaching of Bagasse Kraft Pulp

In order to further reduce absorbable organic halide (AOX) formation in the bleaching effluent, NH2SO3H and DMSO were added during the elemental chlorine-free (ECF) bleaching (D0EpD1) of bagasse kraft pulp. In the D0 stage, AOX formation decreased by 10% with 0.1% NH2SO3H, and a reduction of 11.2% with 1.0% DMSO, respectively. Ultraviolet (UV) spectra, Fourier transform infrared spectroscopy (FTIR), and gas chromatography-mass spectroscopy (GC-MS) were adopted in characterizing changes of lignin degradation and the main functional groups of bleached pulp. The UV spectrum showed that the quantity of polyphenols decreased after adding the additives. The FTIR spectrum showed that both the content of phenolic-type lignin and the degradation degree of lilac-type lignin decreased after adding NH2SO3H. If was found that DMSO was beneficial in retaining C-O-C and C=O structures in cellulose and hemicellulose, while NH2SO3H decreased the content of β-glycosidic bonds and C-O-C structures in cellulose and hemicellulose. The composition of lignin degradation products in the bleaching effluent was analyzed by GC-MS. The contents of chlorobenzene and chlorophenol decreased notably when additives were added. Compared with DMSO, NH2SO3H exhibited poor inhibition on the formation of some phenols.

Effects of additives on absorbable organic halide reduction in elemental chlorine-free bleaching of bagasse kraft pulp

In order to further reduce absorbable organic halide (AOX) formation in the bleaching effluent, NH2SO3H and DMSO were added during the elemental chlorine-free (ECF) bleaching (D0EpD1) of bagasse kraft pulp. In the D0 stage, AOX formation decreased by 10% with 0.1% NH2SO3H, and a reduction of 11.2% with 1.0% DMSO, respectively. Ultraviolet (UV) spectra, Fourier transform infrared spectroscopy (FTIR), and gas chromatography-mass spectroscopy (GC-MS) were adopted in characterizing changes of lignin degradation and the main functional groups of bleached pulp. The UV spectrum showed that the quantity of polyphenols decreased after adding the additives. The FTIR spectrum showed that both the content of phenolic-type lignin and the degradation degree of lilac-type lignin decreased after adding NH2SO3H. If was found that DMSO was beneficial in retaining C-O-C and C=O structures in cellulose and hemicellulose, while NH2SO3H decreased the content of β-glycosidic bonds and C-O-C structures in cellulose and hemicellulose. The composition of lignin degradation products in the bleaching effluent was analyzed by GC-MS. The contents of chlorobenzene and chlorophenol decreased notably when additives were added. Compared with DMSO, NH2SO3H exhibited poor inhibition on the formation of some phenols.

Application of pure, thermostable, alkali-tolerant xylanase in bleaching of oxygen-delignified pine kraft pulp

The effect of oxygen (O2)-delignified pine kraft pulp pretreatment by high-purity, thermostable, and alkaline-tolerant xylanases on elemental chlorine free (ECF) bleaching of O2-delignification kraft pulp was studied. The study found that xylanase pretreatment preserved the intrinsic viscosity and yield of O2-delignified pulp while causing about 7% of delignification with high delignification selectivity. The xylanases with high purity, higher thermostability (75°C~80°C) in highly alkaline media (pH 8.0~9.5) could be applied on an industrial scale. Pulp pretreatment by the high-purity, thermostable, and alkaline tolerant xylanases could improve pulp brightness or reduce the chlorine dioxide (ClO2) consumption. In a D0ED1D2 bleaching sequence using the same amount of ClO2, the xylanase-pretreated pulp obtained a higher brightness (88.2% vs. 89.7% ISO) at the enzyme dose of 2 U/g pulp; or for the same brightness as control (88.2% ISO), the ClO2 dosage in the D0 stage was reduced by 27%, which represents a 16% savings in total ClO2 used for bleaching.

The Impact of Xylanase and Hot Acid Pretreatment on HexAs in Eucalyptus Kraft Pulp Bleaching

The influence of the presence of hexenuronic acid (HexA) in eucalyptus kraft pulp on the efficiency of D0EpD1 was investigated by separately using both commercial cellulase-free xylanase and hot acid pretreatments. In comparison to the xylanase pretreatment, the hot acid pretreatment was more than four-fold effective in removing the HexAs (61%) and concomitantly reduced the kappa number, but resulted in lower viscosity. After subsequent D0EpD1 bleaching, the final brightness and its stability were improved remarkably, especially under xylanase pretreatment. At the same brightness of 85% ISO, the xylanase pretreatment reduced the consumption of active chlorine (35.6%) more than the acid pretreatment did (27.5%). The total relative active chlorine savings for the xylanase pretreatment over the acid pretreatment was therefore nearly 23%. The HexA component can be removed considerably in both D0 and D1 stages during the D0EpD1 bleaching sequence, while only slightly in the Ep stage. The use of xylanase and acid pretreatment both resulted in insignificant physical strength losses for the bleached pulps.