Analysis of Copper(II), Cobalt(II) and Iron(III) Sorption in Binary and Ternary Systems by Chitosan-Based Composite Sponges Obtained by Ice-Segregation Approach

With the intensive industrial activity worldwide, water pollution by heavy metal ions (HMIs) has become a serious issue that requires strict and careful monitoring, as they are extremely toxic and can cause serious hazards to the environment and human health. Thus, the effective and efficient removal of HMIs still remains a challenge that needs to be solved. In this context, copper(II), cobalt(II) and iron(III) sorption by chitosan (CS)-based composite sponges was systematically investigated in binary and ternary systems. The composites sponges, formed into beads, consisting of ethylenediaminetetraacetic acid (EDTA)- or diethylenetriaminepentaacetic acid (DTPA)-functionalized CS, entrapping a natural zeolite (Z), were prepared through an ice-segregation technique. The HMI sorption performance of these cryogenically structured composite materials was assessed through batch experiments. The HMI sorption capacities of CSZ-EDTA and CSZ-DTPA composite sponges were compared to those of unmodified sorbents. The Fe(III) ions were mainly taken up when they were in two-component mixtures with Co(II) ions at pH 4, whereas Cu(II) ions were preferred when they were in two-component mixtures with Co(II) ions at pH 6. The recycling studies indicated almost unchanged removal efficiency for all CS-based composite sorbents even after the fifth cycle of sorption/desorption, supporting their remarkable chemical stability and recommending them for the treatment of HMI-containing wastewaters.

Identification of rock and fracture kinematics in high Alpine rockwalls under the influence of altitude

Alpine environments are characterized by fractured rock. Fractures propagate by weathering processes in a subcritical way, and prepare and trigger rock slope failures. In this study, I investigated (1) the influence of thermal changes on rock kinematics on intact rock samples from the Hungerli Valley, Swiss Alps. To (2) quantify thermal and ice induced rock and fracture kinematics and (3) identify differences of their spatial occurrence, I instrumented crackmeters at intact and fractured rock at four rockwalls reaching from 2585 to 2935 m. My laboratory data shows that thermal expansion follows three phases of rock kinematics: (1) cooling phase, (2) transition phase and (3) warming phase, which result in a hysteresis effect. The cooling phase is characterized by rock contraction, while all samples experienced rock expansion in the warming phase. During the transition phase, rock temperatures differ between rock surface and rock depth, which results in a differentiated response. The dummy crackmeters in the field reflect temperature phases observed in the laboratory and data suggest a block size dependency of the transition phase. In fractured rock, fractures open during cooling and reversely close during warming on daily and annual scale. The dipping of the shear plane controls if fracture aperture decreases with time or increases due to thermal induced block crawling. On seasonal scale, slow ice segregation induced fracture opening can occur within lithology-dependent frost cracking windows. Snow cover controls the magnitude and the number of daily temperature changes, reduces the magnitude of annual cooling but increases the length of the cooling period and, therefore, the potential occurrence of ice segregation. The effects of snow cover increases with altitude due to longer snow duration. Climate change induced warming will shift annual thermal stresses at lower altitudes, however, a shortening of the snow period can increase ground cooling and thermal stress at higher altitudes but also can reduce the length of the ice segregation period. In conclusion, climate change will affect and change rock and fracture kinematics and, therefore, rockfall patterns in Alpine environments.

Modelling frost weathering processes and related stresses in Alpine rockwalls

<p>The periglacial areas of the European Alps are characterised by rugged peaks and steep rockwalls with adjacent scree slopes that reflect high rates of rockfall activity. The current state of knowledge regards ice segregation as the dominant mechanism responsible for the disintegration of rock and associated destabilization of rockwalls. In the present work, we (1) monitored rock temperature in Alpine rock walls, (2) determined rock properties in the laboratory and (3) simulated frost weathering using purely temperature-driven models (Hales and Roering, 2007; Anderson et al., 2013) and physical-based models (Walder and Hallet, 1985; Rempel et al., 2016).</p><p>(1) We monitored rock temperature in 9 rockwalls in the Hungerli Valley and 10 in the Gaisberg Valley at altitudes between 2400 m and 3000 m between 2016 and 2019. Mean annual rock temperature is between -2.8 and 7.9°C and is strongly affected by snow cover, which ranges between 3 and 283 days.</p><p>(2) Lithologies comprise Mica Schist in the Gaisberg Valley and Schisty Quartz Slate with inclusions of Aplite and Amphibolite in the Hungerli Valley. Rock density, seismic and strength properties were quantified in the lab (Draebing and Krautblatter, 2019) to be included in physical-based frost weathering models.</p><p>(3) Frost weathering due to ice segregation can be expressed as cracking intensity, crack growth and porosity change. Our model results show that an annual maximum of cracking intensity, crack growth and porosity change within the first meter of rock depth in the study areas’ rockwalls. Although frost weathering is highly dependent on the thermal distribution inside a rock mass, our data demonstrate that lithological parameters strongly determine frost weathering due to their influence on water migration and fracture toughness. Furthermore, the results suggest that there is no relationship between average annual rock temperature, frost weathering and exposure, a tentative conclusion that is broadly contrary to prevailing consensus.</p><p>In conclusion, rock walls are exposed to strong thermo-mechanical stresses due to ice segregation, which leads to a disintegration of rock and lowering of stability. The present work lends support to other studies, which regard frost weathering as the dominant mechanism responsible for rockfall in mountain periglacial settings.</p><p> </p><p>Anderson, R. S., Anderson, S. P., & Tucker, G. E.: Rock damage and regolith transport by frost: an example of climate modulation of the geomorphology of the critical zone, Earth Surface Processes and Landforms, 38(3), 299-316, 2013.</p><p>Draebing, D., & Krautblatter, M.: The Efficacy of Frost Weathering Processes in Alpine Rockwalls. Geophysical Research Letters, 46(12), 6516-6524, 2019.</p><p>Hales, T. C., & Roering, J. J.: Climatic controls on frost cracking and implications for the evolution of bedrock landscapes. Journal of Geophysical Research-Earth Surface, 112, F02033, 2007.</p><p>Rempel, A. W., Marshall, J. A., & Roering, J. J.: Modeling relative frost weathering rates at geomorphic scales. Earth and Planetary Science Letters, 453, 87-95, 2016.</p><p>Walder, J., & Hallet, B.: A Theoretical-Model of the Fracture of Rock During Freezing. Geological Society of America Bulletin, 96(3), 336-346, 1985.</p>

Fracture dynamics in an unstable, deglaciating headwall, Kitzsteinhorn, Austria

Processes destabilising recently deglaciated rockwalls, driving cirque headwall retreat, and putting high alpine infrastructure at risk are poorly understood due to a lack of in situ monitoring data. Deglaciation initiates internal stress redistribution and drastically increases atmospheric forcing rendering cirque headwalls particularly prone for rock slope failure. Here we present quantitative data from an unstable, recently deglaciated cirque headwall. We monitor the dynamics of a fracture at the north face of the Kitzsteinhorn (3203 m a.s.l.) over a period of 2.5 years. Two crackmeters measure horizontal and vertical crack deformation with a resolution of ±0.003 mm and are complemented by crack top temperature measurements. To decipher thermo-mechanical from cryogenic forcing, thermal expansion coefficients for both horizontal and vertical directions are calculated to derive purely thermo-mechanical deformation. Our data shows that fracture dynamics are dominated by thermo-mechanical expansion and contraction of the inter-cleft rock mass during snow-covered and snow-free periods. Significant deviations from thermo-mechanical behavior occur due to freeze-thaw action during spring and autumn zero curtain periods. Exceptional vertical deformation during these periods is triggered by rainfall events providing liquid water into the fracture system. Subsequent refreezing rather than hydrostatic pressure build-up is to the most likely cause of the mechanical response. Lower magnitude horizontal deformation occurs in autumn and early winter due to ice segregation. Irreversible fracture opening was not observed, however, enhanced cryogenic deformation in spring and autumn may lead to shallow, low magnitude rock detachments. Our results highlight the importance of liquid water intake in combination with subzero-temperatures on the destabilisation of glacier headwalls. We conclude that intense frost action and ice segregation are common processes in randkluft systems, serving as important preparatory factors of paraglacial rock slope instability.