Complex relationships between salt type and rock properties in a durability experiment of multiple salt–rock treatments

A laboratory salt weathering experiment was performed using five salts to attack eight types of rocks to determine the relative significance of rock durability and salt aggressivity to salt crystallization damage. The influence of individual rock properties on the salt susceptibility of the rocks was also evaluated. To study the relation between pore characteristics, salt uptake, and damage, the pre‐ and post‐experiment pore size distributions of the rocks were also examined. It is observed that both salt type and rock properties influenced the damage pattern. The durability ranking of the rocks became significantly altered with the salt type while the variation in salt efficacy ranking with rock type was less pronounced. Of the five salts used, sodium chloride and aluminium sulfate were invariably ineffective with all rock types while sodium carbonate, sodium sulfate, and magnesium sulfate, were markedly more effective in damaging most types of rock used. Of the rock properties investigated, the microporosity (of pores smaller than 0·05 or 0·1 µm) showed the most significant influence on deterioration of the rocks associated with salt crystallization, whereas microporosity of pores smaller than 5 µm played a more important role in salt uptake. Pore size distribution was thus the key factor controlling salt uptake and damage. Rocks with a large number of pores (<5 µm) and a high proportion of pores (<0·05 or 0·1 µm) were particularly susceptible to salt crystallization damage. However, anomalies arose that could not be explained in terms of rock properties or salt efficacy alone. Overall, the relative influences of salt type/efficacy and rock type/properties on salt damage propensity were not clear enough to draw a reasonable conclusion. Salt crystallization damage appears to be influenced by the individual interactions between salts and rocks, which could explain the anomalous results. Copyright © 2009 John Wiley & Sons, Ltd.     

Chemical textures on quartz grains: An experimental approach using salts

Two groups of fresh crushed Brazilian quartz grains (0.4–0.6 mm) were placed in 10 ml of various saturated salt solutions (sodium sulphate, sodium chloride, magnesium sulphate, sodium carbonate, and sodium carbonate and soil). One group was placed in an environmental cabinet programmed to simulate summer diurnal temperature and relative humidity values recorded in Wheeler Valley, a dry valley in southern Victoria Land, Antarctica. The other group was allowed to remain at normal laboratory conditions. Quartz grains from both groups were removed at pre-selected intervals for examination using the scanning electron microscope. After 50 hours chemical surface textures were formed on the quartz grains in all but the sodium sulphate solution. At the 140 hour interval all the salt solutions used were producing chemical surface textures on the quartz grains. This paper demonstrates that chemical surface textures can be produced on quartz grain surfaces by saturated salt solutions in a short period of time and may prove to be representative of chemical surface textures produced in a saturated saline environment.     

Experimental frost and salt weathering of chalk—I

To try to resolve the conflicts surrounding the influence of salts on frost weathering, chalk cubes were immersed, separately, in solutions of sodium chloride, sodium sulphate, and magnesium sulphate at concentrations of 5·5 per cent and 12·5 per cent, in a mixed solution of sodium chloride and sodium sulphate, and in distilled water. The cubes were subjected to six freeze-thaw cycles with temperatures ranging from either +15 to — 10°C or + 15 to — 30°C. The results confirm that frost weathering can be enhanced by the presence of certain salts, but the degree of enhancement depends both on the concentration and type of salt and on the intensity of the freeze-thaw regime. Some, but not all, of the results can be explained by the phase changes that occur during the freezing of the salt solutions.     

Experimental frost and salt weathering of chalk—II

Experiments are described in which chalk cubes were soaked in solutions of either sodium chloride, sodium sulphate, or magnesium sulphate at concentrations of 5·5 per cent and 12·5 per cent, or in a mixed solution of sodium chloride and sodium sulphate or in distilled water. After removal of excess liquid, the cubes were subjected to six freeze–thaw cycles with temperatures ranging from either +15 to ?10°C or +15 to ?30°C. The results confirm that frost weathering can be enhanced by the presence of certain salts, but the extent of weathering was much less than that previously reported for samples frozen totally immersed in the same liquids. Evidence is presented which suggests that salt crystallization is the major weathering process operative when non–immersed samples are frozen but a combination of frost and salt weathering operates when fully immersed samples are frozen.     

Weathering of sandstone by the combined action of frost and salt

Preliminary results from a continuing series of laboratory experiments designed to examine the combined effects of salt and frost weathering indicate that some salts greatly enhance the breakdown of rocks by frost. Samples of Ardingly Sandstone from southeast England were soaked in saturated solutions of sodium chloride or sodium sulphate and subjected to alternating cycles of freezing and thawing. Rapid disintegration of the sandstone occurred within twenty cycles, in each of the salt solutions. In contrast, samples subjected to freezing and thawing in deionized water suffered very little damage unless they were saturated under vacuum. When samples were subjected to twenty cycles of wetting and drying at temperatures above 0°C, those soaked in deionised water or sodium chloride suffered no appreciable damage but those soaked in sodium sulphate rapidly disintegrated. Tentative explanations of these results are offered. The enhancement of frost weathering by salt appears to have been overlooked by many writers yet it is likely to be an important geomorphological process in those areas of mid and high latitudes where rocks are saturated with sodium salts.     

The nature and pattern of debris liberation by salt weathering: A laboratory study

A laboratory simulation of salt weathering was used to ascertain the effects of sodium sulphate and sodium carbonate under ‘Negev’ conditions using a single immersion technique. Three main points were addressed: what are the grain size and textural characteristics of the debris liberated from limestones and a sandstone, what do scanning electron microscope observations of the weathered samples tell us about the decay processes involved, and how does the rate of debris liberation change during the course of 100 cycles? The grain size characteristics of the liberated debris tended to be multimodal and were related to the original petrological characteristics of the rock. Large amounts of fines were produced which are believed to be analogous to the ‘rock flour’ of arid areas. Blistering was also observed. Scanning electron microscope analysis revealed differences in the style of attack for different rock types and salt treatments, and revealed the pattern of salt crystallization in pores and the nature of cracking. The rate of debris liberation tended to decline or remain constant through time. The reasons for this remain obscure, but it is evident that diurnal cycles of temperature and humidity change can cause continuing rock weathering long after the initial input of salt to the rock has taken place.     

Erodibility of some crust forming soils/sediments from the Southern Aral Sea Basin as determined in a wind tunnel

Severe dust storms in the Southern Aral Sea Basin have become common with the desiccation of the sea. The high incidence of dust in the area has had severe ecological consequences. Within the framework of efforts to reduce this phenomenon, deflatability as well as deflatability‐related characteristics of some prominent soils/sediment surfaces in the Southern Aral Sea Basin were examined. The materials included a salt crust from a developed Solonchak, a Takyr crust and a Takyr‐like soil, and salt crusts from undeveloped Solonchaks formed on the exposed bottom of the Aral Sea. Characteristics determined were particle size distribution, dry aggregate size distribution and salt, carbonate and organic carbon contents. Deflatability was examined using a suction type wind tunnel with a SENSIT‐type sensor to detect airborne unconsolidated material, on materials treated to different moisture levels and with a chemical stabilizer, and on restored crusts created from the unconsolidated materials. Fine sand dominates in the materials, and in the Takyr crust and Takyr‐like soils is accompanied by significant amounts of silt and clay. All materials contain moderate amounts of carbonate and are low in organic matter. All soils/sediments contain salts, but in the salt crusts of the Solonchaks the salt fraction dominates. They all have more than 50 per cent PM₈₅₀ (particles with diameter <850 µm), indicating a relatively high deflatability potential. The materials from the Takyr crusts and Takyr‐like soil with a high proportion of fine aggregates had the lowest threshold friction velocities, while the salt crusts of the Solonchaks with a high proportion of coarse aggregates had the highest. This suggests that Takyrs and Takyr‐like soils are the most deflatable and Solonchak soils the least deflatable. These differences are attributed to the presence of salts that create stable, large aggregates in the Solonchak crusts. Wetting of the materials to three moisture levels considerably increased threshold friction velocity. The increase was most prominent in the salt‐rich materials, and was attributed to the rapid formation of surface films by drying in the course of the wind tunnel determinations. Applications of chemical stabilizers at two levels also considerably increased threshold friction velocity. On the restored crusts, threshold friction velocity dramatically increased, occasionally to non‐recordable values. This increase was monitored with both the salt crusts characteristic for the Solonchak soils and the fine‐grained crusts characteristic for the Takyr soils. The stability was attributed to the tightly packed salt particles in the salt crusts, and to the cohesive properties of the fine‐grained materials in the Takyr crusts. Once the crusts were ruptured, however, strong deflation commenced. These results suggest that by maintaining moisture in the soils/sediments (for example, by maintaining a high water table in the Amu‐Darya river flood plain) deflation can be reduced. By the same means, deflation can be reduced by creating new crusts or by preserving existing crusts. Copyright © 2005 John Wiley & Sons, Ltd.     

Geochemische und 13C/12C-isotopenchemische Untersuchung zur Herkunft der Kohlensäure in mineralhaltigen Wässern Nordhessens (Deutschland)

Geochemical and ¹³C/¹²C-isotopical Investigation of Mineral Waters in Northern Hessia (Germany) and the Origin of their CO₂ Content The dissolved carbonate originates from three sources: 1. biogenetic soil-CO₂, 2. volcanic CO₂ related to the evaporites of the Zechstein formation, and 3. carbonate derived from the dissolution of limestones and dolomites. Miocenic basaltic melts penetrated the evaporites of the Zechstein, and the related CO₂ was trapped in the intra- and intergranulars of the salt minerals. Circulating meteoric waters dissolve the salt minerals releasing CO₂ gas. Thus, the occurrence of basalt is related to the CO₂ contents of the evaporites, and the dissolution of only small amounts of salts rich in CO₂ may result in a high concentration of carbonic acid. In waters rich in carbonate, where volcanic CO₂ dominates over the other two sources of carbon, a δ¹³C-value of “salt-CO₂” of about –1‰ (PDB) is obtained. Water with less dissolved carbonate species have smaller quantities of salt-CO₂ down to about 20%.     

Contour scaling of a sandstone by salt weathering under simulated hot desert conditions

A laboratory study has been used to investigate relationships between salts and contour scaling—a weathering feature commonly observed on rock surfaces in salt-rich environments. Surface disaggregation and essentially surface-parallel cracks were produced in sandstone blocks using 10 per cent solutions of sodium sulphate and magnesium sulphate applied daily to single exposed surfaces for sixty days. A control block soaked once in saturated magnesium sulphate and subsequently wetted daily with distilled water showed extensive surface disaggregation, but no cracking. Both surface disaggregation and subsurface cracking were associated with relative concentrations of microcrystalline salt. A tentative model of contour scaling is proposed, which involves linking together potential cracks by salt-induced fracturing of intervening, crack-stopping grains. Further control blocks treated respectively with 10 per cent and saturated sodium chloride showed no evidence of subsurface cracking and only limited surface disaggregation of the ‘saturated’ block.     

Evolution of the Subsurface K‐Rich Brines in the Triassic Carbonates in the Sichuan Basin of China

Subsurface K‐rich brines are important mineral resources for fertilizer production while the evolution of such brines is poorly documented. In the Sichuan Basin in southwest China, they are found mainly in the Middle and Lower Triassic marine carbonate aquifers. Total dissolved solids of the brines range from 176 to 378 g/L and K concentrations, from 1.9 to 53.3 g/L. We found that the brines are mainly of Cl‐Na type, while Ba is absent in the brines. Comparison of the brine samples with both the trajectories of ions and the newly proposed trajectories of ion ratios of evaporated seawater suggests that the brines are enriched in Ca, Sr, Li, and I, depleted in SO₄ and Mg, and neither enriched nor depleted in Cl and Na. These brines underwent four evolutionary periods: (1) deposition of marine rocks, (2) deposition of continental clastics, (3) tectonic deformation, and (4) rock erosion. Precipitation of salt minerals, dolomitization, sulfate reduction, and recrystallization during the first two periods are responsible for the enrichment and depletion of the chemical constituents of the brines. Extremely high K concentrations in two wells, both tapping the Middle Triassic Leikoupo carbonate aquifers, are attributed to the subsurface dissolution of potash salts during the migration of the brines to the anticlines formed during the third period in the Paleogene age. Saline and salty springs emanate from the outcropping carbonates in the river valleys in some anticlines in the eastern basin due to incongruent dissolution of the salt‐bearing carbonates during the fourth period.     

Effects of Deicing-Salts on Heavy Metal Mobility Zum Einfluß von Streusalzen auf die Beweglichkeit von Schwermetallen

Heavy metal input into roadside soils and effects of deicing salts are often discussed as separate environmental problems. However, a relationship between salt input and heavy metal mobility has already been detected in laboratory tests. During a 2-year field study, the soil solution of a roadside soil was continuously sampled. The results of soil solution analysis not only showed a strong rise in deicing-salt related sodium, calcium and chloride concentrations, but also high zinc and cadmium values in winter and spring. Additional laboratory tests confirmed the mobilizing effects of salt solution which contained NaCl and CaCl₂. Cation exchange and the formation of chlorocomplexes are discussed as the responsible mechanisms.     

The Origin and Distribution of Salts on Alluvial Fans in The Atacama Desert,Northern Chile

The Atacama Desert has been predominantly hyperarid since the middle Miocene. Combined ionic and X-ray diffraction analysis shows that calcium sulphate is prevalent on three similar alluvial fans in salar basins across a transect of different environments in Antofagasta Province, northern Chile. Differences between the fans were largely due to the effect of local factors on salt input, secondary redistribution and deposit preservation. Thus carbonate was notable in the High Andes (fan C) and Pre-Cordillera (fan B), whereas in the Central Valley (fan A) greater qualities of the more soluble salts (chlorides and nitrates) probably reflect the higher level of aridity and an oceanic source (the camanchaca). Calcium sulphate distribution on the alluvial fans and on adjacent hilltops indicates an aeolian origin. Evidence from the Pre-Cordillera (fan B), however, suggests that salt input may have been episodic, related to changes in conditions within the general aridity and possibly to stone pavement and soil development. Calcium sulphate sources range from an input in Andean precipitation and the camanchaca to abundant regional evaporite deposits. It is probable, however, that products of Andean volcanism constitute the dominant primary source of calcium sulphate, and that the salt has subsequently been distributed widely within the endoreic basins of the region by a combination of groundwater, surface flow and the wind. © 1997 John Wiley & Sons, Ltd.     

Determination of Cu,Fe, and Ni in Spices after Preconcentration on Diaion‐HP 20 Resin as Their Zincon Complexes

In this work, a new separation–preconcentration method was developed for the determination of trace amounts of Cu(II), Ni(II), and Fe(III) by flame atomic absorption spectrometry (FAAS). Analytes were complexed by using zincon (2‐[2‐[alpha(2‐hydroxy‐5‐sulfophenylazo) benzylidene] hydrazino] benzoic acid sodium salt). The analyte ions were quantitatively adsorbed on a Diaion HP‐20 resin at pH 5. The retained metal ions on the resin were eluted by acetone. The analytical parameters such as pH of the sample, eluent type and volume, sample volume, and flow rates of the solution and the eluent were investigated. The influences of concomitant ions on the recoveries of the analytes were also examined. The instrumental detection limits for the analytes after application of the presented solid‐phase extraction procedure were in the range of 0.72–1.41 µg/L. The validation of the presented procedure was checked by analyzing certified reference material of SRM1515 Apple Leaves. The procedure was performed by analyzing some spice samples.     

DC GEOELECTRIC SOUNDING TO DETERMINE WATER CONTENT IN THE SALT MINE ASSE (FRG)*

In the course of investigations concerning disposal of radioactive waste, DC-geoelectric soundings were performed in the salt mine Asse in 1982. The survey resulted in the determination of resistivities of various salt formations. A comparison of various resistivities obtained in salt formations in the mine shows that it is possible to estimate the content of free water in salt using Archie's equation. The significant result of this survey is that salt formations in the mine can be divided into two categories according to their resistivities: 1. Salt with resistivity between 10⁷ and 10⁸Ωm (particularly Na2Sp and Na3β). The particularly pure halitic formations are to be found within this resistivity range. 2. Salt with resistivity between 10³ and 10⁵Ωm (Na2Tl, K2, transition salt). The salt formations with thin layers of anhydrite and a high content of hygroscopic salts are classified in the paper.     

Seismic time‐lapse effects of solution salt mining – a feasibility study

This article addresses the question whether time‐lapse seismic reflection techniques can be used to follow and quantify the effects of solution salt mining. Specifically, the production of magnesium salts as mined in the north of the Netherlands is considered. The use of seismic time‐lapse techniques to follow such a production has not previously been investigated. For hydrocarbon production and CO₂ storage, time‐lapse seismics are used to look at reservoir changes mainly caused by pressure and saturation changes in large reservoirs, while for solution mining salt is produced from caverns with a limited lateral extent, with much smaller production volumes and a fluid (brine) replacing a solid (magnesium salt). In our approach we start from the present situation of the mine and then study three different production scenarios, representing salt production both in vertical and lateral directions of the mine. The present situation and future scenarios have been transformed into subsurface models that were input to an elastic finite‐difference scheme to create synthetic seismic data. These data have been analysed and processed up to migrated seismic images, such that time‐lapse analyses of intermediate and final results could be done. From the analyses, it is found that both vertical and lateral production is visible well above the detection threshold in difference data, both at pre‐imaging and post‐imaging stages. In quantitative terms, an additional production of the mine of 6 m causes time‐shifts in the order of 2 ms (pre‐imaging) and 4 ms (post‐imaging) and amplitude changes of above 20% in the imaged sections. A laterally oriented production causes even larger amplitude changes at the edge of the cavern due to replacement of solid magnesium salt with brine introducing a large seismic contrast. Overall, our pre‐imaging and post‐imaging time‐lapse analysis indicates that the effects of solution salt mining can be observed and quantified on seismic data. The effects seem large enough to be observable in real seismic data containing noise.     

‘frost and salt’ weathering: Further experimental results

A laboratory experiment has been conducted to examine the effects of ‘frost and salt’ weathering (i.e. physical breakdown by the freezing of salt solutions) on a limestone. Results show that the presence of certain salts in solution can inhibit frost damage. These findings are in direct conflict with those presented by Goudie (1974) and, more recently, Williams and Robinson (1981). Comparison of the experimental methods used in each of these three studies suggests that opposing results can be explained in terms of the different experimental procedures which were employed. If salt supply is frequent and plentiful then it seems likely that rock breakdown will be enhanced-this is the case represented by the experiment of Williams and Robinson. Conversely if the salt supply is limited and the amounts of salt remain more or less constant then rock breakdown will be inhibited-the case of the present experimental study. Caution is therefore advocated when attempting to extrapolate laboratory-derived results to infer on the behaviour of rocks under natural conditions. Several environmental situations in which ‘frost and salt’ weathering may be a possibility are dsiscussed, but it is concluded that further field data, especially concerning temperature regimes and salt availability at and below rock surfaces in cold regions, would be necessary before more definite statements could be made about the efficacy of this process.     

Regional‐scale investigation of the spatial distribution and origin of soluble salts in central north Queensland

A method for regional assessment of the distribution of saline outbreaks is demonstrated for a large area (68 000 km²) in north Queensland, Australia. Soil samples were used in conjunction with a digital elevation model and a map of potentially saline discharge zones to examine the landscape distribution of soluble salts in the region. The hypothesis of atmospheric accession of salt was tested for the topographically defined catchment regions feeding into each potentially saline discharge area. Most catchments showed a salt distribution consistent with this hypothesis, i.e. %TSS was large near the discharge areas and decreased rapidly with distance uphill from the discharge areas. In some catchments, however, local saline outbreaks were apparent at significant distances uphill from discharge areas. The possibility of geological sources of this salt was examined by comparing random point distributions with the location of saline points with distance downhill from geological units (excluding points near discharge zones). The distribution of some saline outbreaks was consistent with the occurrence of Cambro‐Ordovician metasediments, Devonian limestone, Upper Devonian–Lower Carboniferous volcanics, and Triassic sediments. Copyright © 2000 John Wiley & Sons, Ltd.     

An investigation into the relationship between salt weathering debris production and temperature

An investigation using laboratory simulation has been made using air temperature data for Tunisia, Antarctica, and southwest England. An experiment with a 50 cycle run produced results which showed significantly greater debris production in the Antarctica and Tunisian simulations than in the southwest England simulation. Using X-ray analysts to determine salt penetration, an inverse relationship between salt penetration and debris production was seen to exist. This could be the result of evaporation in the Tunisian simulation and rapid freezing in the Antarctic simulation, concentrating salts in the upper layers of the rock samples. In the southwest England simulation, no freezing, and relatively high humidities allowed greater penetration, thus distributing an equal input of salt over a greater area. The author tentatively suggests the possible existence of a parabolic relationship between salt weathering and temperature.     

Laboratory simulation of the salt weathering of schist: II. Fragmentation of fine schist particles

Recent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data, and in particular data describing the size distribution of the weathered rock fragments. To enable future development of rock breakdown models for use in landscape evolution and soil production models, laboratory work was undertaken to extend existing schist/salt weathering fragmentation studies to include an examination of the breakdown of sub‐millimetre quartz chlorite schist particles in a seasonally wet tropical climate. Laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution. The results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown. The fragmentation of the schist is characterized by splitting of the larger fragments into mid‐sized product with finer material produced, possibly from the breakdown of mid‐sized fragments when weathering is more advanced. Salinity, the salt addition method and temperature were all found to affect weathering rates. Subtle differences in mineralogy also produce variations in weathering patterns and rates. It is also shown that an increase in drying temperature leads to accelerated weathering rates, however, the geometry of the fracture process is not significantly affected. Copyright © 2006 John Wiley & Sons, Ltd.     

Salt weathering: influence of evaporation rate,supersaturation and crystallization pattern

Micro- and macroscale experiments which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations. Previously unexplained differences are found in crystal morphology, crystallization patterns, kinetics and substrate damage when comparing the growth of mirabilite (Na₂SO₄. 10H₂O) and thenardite (Na₂SO₄) versus halite (NaCl). The crystallization pattern of sodium sulphate was strongly affected by relative humidity (RH), while a lesser RH effect was observed for sodium chloride. Macroscale experiments confirmed that mirabilite (crystallizing at RH > 50 per cent) and thenardite (crystallizing at RH < 50 per cent) tend to form subflorescence in highly localized areas under conditions of constant RH and temperature. This crystallization pattern was more damaging than that of halite, since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion, a result which contradicts Wellman and Wilson's theoretical model of salt damage. Low RH promoted rapid evaporation of saline solutions and higher supersaturation levels, resulting in the greatest damage to the stone in the case of both sodium sulphate and sodium chloride crystallization. At any particular crystallization condition, sodium chloride tended to reach lower supersaturation levels (resulting in the crystallization of isometric crystals) and created negligible damage, while sodium sulphate reached higher supersaturation ratios (resulting in non-equilibrium crystal shapes), resulting in significant damage. ESEM showed no damage from sodium sulphate due to hydration. Instead, after water condensation on thenardite crystals, rapid dissolution followed by precipitation of mirabilite took place, resulting in stone damage by means of crystallization pressure generation. It is concluded that salt damage due to crystallization pressure appears to be largely a function of solution supersaturation ratio and location of crystallization. These key factors are related to solution properties and evaporation rates, which are constrained by solution composition, environmental conditions, substrate properties, and salt crystallization growth patterns. When combined with a critical review of salt damage literature, these experiments allow the development of a model which explains variations in damage related to combinations of different salts, substrates and environmental conditions. Copyright © 1999 John Wiley & Sons, Ltd.