Tanning Solutions Research Articles

Review: Leather sustainability, an industrial ecology in process

AbstractLeather production is a historic industry that still has an economic influence throughout the world. Leather making is done following a sequence of complex chemical and mechanical steps, using energy, quantity of water and chemicals, and generating waste. For several decades, many organizations have been working toward a cleaner tannery industry resulting in better practices, saving energy and water, and increasing wastewater treatment efficiency. Solid waste management remains a big issue. Another question posed today is the use of chromium in tanning. It is why a lot of research is now dedicated to metal‐free tanning solutions. Chromium alternatives exist but none can actually rival all the advantages of chromium and a balance must be found with environmental issues. To measure the environmental performance of leather, several tools are available. The LWG (Leather Working Group) audit is one of them. On the side of consumers, some reliable leather ecolabelings exist. Finally, life cycle assessment (LCA) is the most exhaustive tool for characterizing leather's environmental performance. Numerous LCA studies done in the past two decades underline the difficulty in obtaining general results, considering the large variety of processes used depending on tanneries, localization, and raw materials. In addition, the data available for LCA are still poor in regard to the specific data needed for leather chemicals. The best methods associated with new technologies, audit, and labeling lead leather production into a cleaner and environment‐friendly industry.

Devising techniques for reinforcing glued sausage casings by using different physical methods

This paper has substantiated the development and rationalization of techniques to manufacture sausage casings from natural raw materials with predefined functional and technological properties. It is noted that the issue related to the rational utilization of intestinal raw materials and the improvement of the production economic profitability could be resolved by implementing effective technologies of glued intestinal sausage casings.
 The strength has been investigated of the reinforcing seam between the layers of intestinal membranes obtained by such techniques as the local tanning, local thermal coagulation resulting from passing an electric current through wet raw materials, local thermal coagulation due to the arc discharge through dried raw materials.
 The rational concentration of tannin in tanning solution has been determined, at which it is recommended to make a reinforcing seam on glued intestinal casings by means of local tanning. A value of the breaking load for the reinforcing seam made by using local electric currents has been derived, which is 14 N/m. A 4.7-time increase in the breaking load has been established to occur, compared to the control sample. A value of the breaking load for the reinforcing seam obtained by applying an arc discharge has been found, which is 18 N/m. It was noted that the breaking load had increased compared to the control sample.
 Working bodies for an installation were designed aimed at reinforcing glued sausage casings by such techniques as local tanning; local thermal coagulation resulting from passing an electric current through wet raw materials; local thermal coagulation as a result of arc discharge through dried raw materials. It is noted that the advantages of techniques for the reinforcement of glued sausage casings are the high breaking load and the effective utilization of raw materials

PREPARATION OF MIXED HYDROGELS BASED ON BIOPOLYMERS AND THE STUDY OF THEIR RHEOLOGICAL PROPERTIES

A well-known, affordable, and cheap method of modifying biopolymers is their simple mixing with synthetic and natural polymers. As a result, similar to metal alloys, polymer-polymer complexes with predetermined properties can be obtained. Although interpolymer complexes became a subject of study and application a long time ago, in domestic practice, the study of natural biopolymers is limited. The purpose of this study was to present and study the issue of structuring in solutions of bio- and synthetic polymers, as with a low dry matter content such structures have many properties of a solid. Natural ampholytic polymers are polyelectrolytes, which is also of great importance for their further study. By analyzing the results of studies of complexes formed by a synthetic linear polyelectrolyte with a charged partner – protein, it becomes possible to create new “smart” polyelectrolyte complexes that can undergo phase changes in narrow, controlled pH ranges. The positive effect of sodium carboxymethyl cellulose on the gelation of 5% gelatine hydrogels was established. It was determined that the presence of additives of inorganic salts leads to an increase in the swelling of gelatine gels. It was established that more durable gels are less prone to aging. The practical significance of these studies is determined by the fact that in many industries (food, soap, paint, and varnish), it is necessary to obtain structures with tailor-made properties. Gel formation may also be an undesirable phenomenon that must be prevented, for example, in the production of chemical fibers, glues, and tanning solutions. Furthermore, biological objects themselves in most cases, by their nature, are protein gels with specific mechanical properties. Keywords: structure and dynamics of gelatine mixed hydrogels, adsorption on solid surfaces, collapse of heterogeneous networks, swelling and aging of mixed gelatine hydrogels.

Fast high-pressure tanning of animal skins by accelerated chromium sulphate complexation

In the conventional leather production process, basic chromium sulphate (BCS) penetrates fully inside the collagen matrix during tanning and forms oligo-nuclear complexes that stabilize the skin structure during basification. Accelerated chromium sulphate complexation by basifying the BCS before full penetration leads to surface tanning and low leather qualities. Therefore, long processing times of 16 h for tanning and basification are common in modern tanneries. We used sodium hydrogen carbonate to basify BCS before penetration. However, instead of conventional tanning we performed CO2 tanning at 30 bar. The influence of accelerated chromium sulphate complexation on the leather quality was investigated. To estimate the structures of the formed chromium complexes, we considered the pH trend of the tanning solution during basification depending on the amount of basifying agent. The distribution of chromium oxide (Cr2O3) and the shrinkage temperature (Ts) in three different layers of the cross section were analysed. The analytics allowed the assessment whether the tanning agent penetrates through the whole cross section or adheres to the surface during CO2 tanning. We show that CO2-intensified tanning allows accelerated chromium sulphate complexation and a reduction in the tanning time from 16 to 4 h. The Cr2O3 is equally distributed, and Ts above 100 °C meets the standards of high-quality wet blue. However, the pH value of the tanning solution must not rise above 4.5 during basification. Otherwise, the Ts decrease dramatically. The feasibility of the process is demonstrated in a 1700-L drum, with a batch size of about 500 kg. The CO2-intensified tanning process has high potential to save time and chemicals and reduce emissions in industrial applications and is commercially competitive.Graphic abstract

Electrochemically Enhanced Processes for Leather Tanning

Leather production involves several operations where the tanning plays the major role in improving the durability of leather products by forming durable linkages between the tanning agents and the collagen. Different agents are used, but the most important is chromium. However, nowadays there is a growing demand for a cleaner, but still effective alternative for production processes. In the traditional tanning process, the penetration of these agents inside the leather is governed by diffusion based on a concentration gradient. In this study, a new tanning approach is proposed, taking advantage of the intensification effects of an applied electric field, within two electrodes in solution, on the tanning method [1]. An improvement in the efficiency is observed due to the positive charge acquired by the agents (Cr, Ti, Zr and Fe) complexes in tanning solutions and the possibility to control the bath pH by exploiting the side reactions at the two electrodes. The new electrochemically intensified tanning technique shows better performances than the standard one, resulting in a larger agent uptake in the same amount of time, leading to a shorter process time. The intensification of the tanning process will be justified in light of a simulation model of the involved phenomena. Enhanced chrome tanning process, Patent Pending

PRECIPITATION OF CHROMIUM-CONTAINING TANNING SOLUTION OF SUSPENSION MAGNESIUM HYDROXIDE

Comparative studies of the deposition of tanning chromium compounds from waste tanning solutions of tannery production containing from 3 to 5 g/l chromium oxide were carried out, using as a chemical reagents a suspension of magnesium hydroxide and sodium carbonate solution. It is shown that the main factors influencing the precipitation process are the pH value and the consumption of the precipitant. The costs of reagents contributing to complete precipitation of chromium compounds in the form of a hydroxide are established. The high efficiency of the use of a suspension of magnesium hydroxide as a precipitator is shown, due to the higher deposition rate and the absence of chromium compounds in the supernatant. The rate of precipitation of chromium using a slurry of magnesium hydroxide is 4.9 cm3/min, and using sodium carbonate 2.5 cm3/min. In the supernatant, after precipitation with sodium carbonate, traces of chromium oxide are found - less than 2.53 g/l. It is shown that when using a suspension of magnesium hydroxide for the precipitation of chromium, periodic mixing of the liquid is necessary to more completely dissolve the precipitator, which in the first stage after dosing drops out of the solution as a precipitate. When sodium carbonate is used, the formation of hydroxyl ions occurs much faster than in the case of a suspension of magnesium hydroxide. However, the formed sediment has a rather loose structure and is characterized by a high moisture content. The precipitate of chromium hydroxide obtained by using a suspension of magnesium hydroxide is characterized by a higher density and better filtration ability. A gradual increase in pH during the precipitation of a tanning solution with a suspension of magnesium hydroxide results in a precipitate with a large particle size and lower humidity.

Enhanced release of palladium and platinum from catalytic converter materials exposed to ammonia and chloride bearing solutions.

The environmental levels of platinum group elements (PGEs) are steadily rising, primarily due to exhaust emissions of vehicle catalytic converter (VCC) materials containing solid PGEs. Once these VCC materials reach soil and water, the PGEs may be transported in the form of nanoparticles (dimensions 1-100 nm) or they may be mobilized by forming coordination complexes with ligands in the environment. Chloride (Cl-) and ammonia (NH3) are two ligands of particular concern due to their ubiquity as well as their potential to form the chemotherapy drug cisplatin (Pt(NH3)2Cl2) or other potentially bioactive complexes. This initial study examines the release of Pd and Pt into solutions exposed to VCC materials at pH 8 and 25 °C, using elemental analysis of metal content in post-exposure extracts. The solutions had total ammonia nitrogen concentrations (TAN, [NH4+] + [NH3]) of 0 μM, 5.56 μM, 55.6 μM and 1.13 × 105 μM (0 ppm, 0.1 ppm, 1 ppm, and 2147 ppm). The former three represent background environmental levels had a minimal effect on release. However, when combined with 1.13 × 105 μM Cl- (4000 ppm Cl-), 55.6 μM TAN induced a marked increase in metal release (∼41× for Pd). High TAN solutions induced more Pd and Pt release than equimolar NaCl solutions. Materials characterization revealed that ∼4 nm palladium-containing nanoparticles were present, spatially associated with nanoparticles of γ-Al2O3; ceria-zirconia nanoparticles were also present but did not have any metal associated with them. Platinum-containing nanoparticles were not observed.

Electrochemical treatment of spent tan bath solution for reuse

Abstract A spent tanning bath contains high concentration of salts, chromium and protein. The treatment system for removal of chlorides or chromium from this effluent is expensive. In this context this waste has to be reused. Our study focuses on the application of advanced oxidation processes for protein removal present in a tanning bath. To improve the quality of the chromium tanning bath, two electrochemical processes (electrooxidation and peroxi-electrocoagulation process, PEP) are investigated in a batch reactor. The effects of operational parameters such as reactor configuration, current density and electrolysis time on chemical oxygen demand (COD) and protein removal efficiency are examined. Results indicated that under the optimum operating range for process, the COD and protein removal efficiency reached 53 and 100%, respectively. The optimum values are determined for the hybrid process (PEP) under 0.13 A·cm−2 over 2 h. The treated tanning bath is used as a tanning solution in leather processing. The influence of chromium salt dose, pH solution, stirring time and contact time on the leather characteristic is evaluated. The hides tanned after the addition of 0.25% of commercial chromium salt, at pH solution, leaving them stirring for 4 h with a contact time of 2 days, and showed good hydrothermal stability and physical characteristics of leather.

Chemical exposures and risk of acute myeloid leukemia and myelodysplastic syndromes in a population-based study.

Benzene exposure is one of the few well-established risk factors for myeloid malignancy. Exposure to other chemicals has been inconsistently associated with hematologic malignancies. We evaluated occupational and residential chemical exposures as risk factors for acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) using population-based data. AML and MDS cases were identified by the Minnesota Cancer Surveillance System. Controls were identified through the Minnesota driver's license/identification card list. Chemical exposures were measured by self-report. Unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CI). We included 265 MDS cases, 420 AML cases and 1388 controls. We observed significant associations between both MDS and AML and benzene (OR = 1.77, 95% CI 1.19, 2.63 and OR = 2.10, 95% CI 1.35, 3.28, respectively) and vinyl chlorides (OR = 2.05, 95% CI 1.15, 3.63 and OR = 2.81, 95% CI 1.14, 6.92). Exposure to soot, creosote, inks, dyes and tanning solutions and coal dust were associated with AML (range ORs = 2.68-4.03), while no association was seen between these exposures and MDS (range ORs = 0.57-1.68). Pesticides and agricultural chemicals were not significantly associated with AML or MDS. Similar results were observed in analyses stratified by sex. In addition to providing risk estimates for benzene from a population-based sample, we also identified a number of other occupational and residential chemicals that were significantly associated with AML; however, all exposures were reported by only a small percentage of cases (≤10%). While chemical exposures play a clear role in the etiology of myeloid malignancy, these exposures do not account for the majority of cases.

Abstract 3427: Chemical exposures and risk of acute myeloid leukemia and myelodysplastic syndromes in a population-based study

Abstract Background Myelodysplastic syndromes (MDS) are a group of clonal hematologic disorders that result in ineffective hematopoiesis. Individuals with MDS have a high risk of progressing to leukemia, with approximately 30% expected to develop acute myeloid leukemia (AML). Benzene exposure is one of the few well-established risk factors for AML, and recent studies suggest it is also a risk factor for MDS. Exposure to other occupational and residential chemicals has been inconsistently associated with hematologic malignancies. In this analysis, we evaluated occupational and residential chemical exposures as risk factors for AML and MDS using population-based data. Methods AML and MDS cases were identified by rapid case ascertainment through the Minnesota Cancer Surveillance System (MCSS). Centralized pathology and cytogenetics reviews were conducted to confirm diagnosis and classify by subtypes. Controls were identified through the Minnesota State driver's license/identification card list. Chemical exposures were measured by self-report and included occupational and residential exposure to a variety of chemicals. Unconditional logistic regression with adjustment for age, sex, previous cancer treatment, income, and farm or rural residence was used to calculate crude and adjusted odds ratios (ORs) and 95% confidence intervals (CI). Smoking, obesity and physical activity were considered as potential confounders but did not change effect estimates by 10% or more. Results We included 265 MDS cases, 420 AML cases, and 1388 controls in this analysis. As expected, we observed significant associations between benzene and both MDS and AML (OR = 1.77, 95% CI 1.17, 2.67 and OR = 2.03, 95% CI 1.45, 2.83, respectively). Exposure to vinyl chlorides was associated with MDS (OR = 2.25, 95% CI 1.32, 3.81) but not with AML (OR = 1.36, 95% CI 0.83, 2.21). Exposure to fertilizers (OR = 1.70, 95% CI 1.11, 2.59), soot (OR = 2.64, 95% CI 1.59, 4.39), creosote (OR = 1.95, 95% CI 1.08, 3.51), inks, dyes and tanning solutions (OR = 1.63, 95% 1.02, 2.60), and coal dust (2.64, 95% CI 1.30, 5.39) were associated with AML, while no association was seen between any of these exposures and MDS (range ORs = 0.78-1.25). No significant associations were observed for occupational pesticide exposures in either group. Discussion These data confirm the importance of benzene as a risk factor for myeloid malignancy and provide risk estimates in a population-based sample. A number of other significant associations with occupational and residential chemicals were observed for AML; however, all exposures were reported by only a small percentage of cases (≤10%). While chemical exposures play a clear role in the etiology of myeloid malignancy, these exposures do not account for the majority of cases. Citation Format: Jenny N. Poynter, Michaela Richardson, Michelle Roesler, Cindy K. Blair, Betsy Hirsch, Phuong Nguyen, Adina Cioc, James R. Cerhan, Erica Warlick. Chemical exposures and risk of acute myeloid leukemia and myelodysplastic syndromes in a population-based study. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3427.

Microscopic changes induced by Cr-Vi in spleen of albino mice

Chromium is believed to be an essential trace element in human nutrition. Evidence suggests that it plays an important role in normal carbohydrate metabolism. It was found that patients receiving long-term total parenteral nutrition (TPN) without chromium developed glucose intolerance, weight loss and peripheral neuropathy Chromium is present in a normal diet at trace (but essential) levels. Occupational exposure is related to the industrial uses of chrome compounds in production and use of steels, pigments, leather tanning and wood preservation solutions, plating chemicals, and cement. Toxicity is predominantly associated with industrial exposures. Hexavalent chromium compounds appear to have greatest toxicity and almost all tissues of body are affected. To evaluate the effects on lymphoid tissue, present study was carried out. The mice of experimental group (2wks, 4wks, 6wks and 8wks) were injected Potassium dichromate (K2Cr2O7) intraperitoneally according to experimental design. The drug caused slight to marked hyperplasia of lymphoid follicles and dilatation of sinuses of red pulp depending upon duration of exposure. Aggregates of hemosidrin-laden macrophages were also seen indicating heamolytic effects on RBCs.

Severe burn on 81% of body surface after sun tanning

We report herein the case of a 42-year-old woman who presented to the Burns Unit with 81% of her body surface severely burned following sun bathing, after applying fig leaf tea as a tanning agent. The patient was hospitalized for 13 days in a Burns Intensive Care Unit, and was discharged for an ambulatory follow-up. The treatment of such burns does not differ from any conventional treatment for heat- induced second-degree burns. The physiopathology of the phytophotodermatitis induced by such homemade tanning solutions rich in psoralen is discussed in detail.

Recycling spent solutions from chrome tanning in leather production

A study has been made on the destruction of dissolved organic impurities in spent tanning solutions by the use of Fenton's reagent. The results indicate that these spent solutions can be regenerated without precipitating chromium hydroxide.

Integrated Membrane Process for the Recovery of Chromium Salts from Tannery Effluents

Conventional chrome tanning in leather production produces spent liquors containing significant amounts of chromium and other polluting substances, both organic and inorganic. The aim of this study was to identify a technically viable method for recovering chromium salts from spent tanning liquors. For this purpose, an integrated process based on a preliminary ultrafiltration (UF) treatment of the spent liquor followed by a nanofiltration (NF) treatment of the UF permeate was studied on the laboratory scale. The UF process permitted a marked reduction of suspended solids and fat substances to be obtained. A tanning solution with a chromium(III) concentration of about 10 g/L was obtained in the NF process. The concentrated chromium solutions were used in experimental trials of chrome tannage performed on pickled sheepskins (experimental group). Their properties were compared with those of skins (control group) treated with the conventional method using basic chromium sulfate powder. The NF retentate seems to guarantee improved characteristics of the tanned skins with respect to the control group. Furthermore, a higher percentage of chromium depletion was observed for the tanning operation performed with the NF retentate. The process also permitted the reuse of the NF permeate in the pickling step because of its high content of chlorides.

Chromium (III) Removal and Recovery from Tannery Wastewater by Precipitation Process

Chromium (III) salts are the most widely used chemicals for tanning processes, but 60-70% of total chromium salts reacts with the hides. In the other word, about 30-40% of the chromium amount remains in the solids and liquid wastes (especially spent tanning solutions). Therefore, the removal and recovery of the chromium content of these wastewaters are necessary for environmental protection and economic reasons. Removal and recovery of chromium were carried out by using precipitation process. For this purpose, three precipitating agents calcium hydroxide, sodium hydroxide and magnesium oxide were used. The effects of pH, stirring time, settling rate and sludge volume were studied in batch experiments. Results show that the optimum pH is 8-9 and the good sludge with high settling rate and lower volume obtain by the MgO precipitating agent. Hence the MgO is a good precipitating agent for removal and recovery of chromium from tanning wastewater.

Spray-on tanning

The modern formulation of dihydroxyacetone (DHA), the only sunless tanning solution approved by the Food and Drug Administration (FDA), is combined with bronzers and moisturizers to deliver a cosmetically acceptable skin color and a natural-looking tan without ultraviolet (UV) exposure. Spray-on tanning products, which deliver this formulation evenly to achieve a full body tan, may be applied in a tanning booth, airbrushed on by a technician, or sprayed on at home, and they appear to offer a generally safe alternative for patients who seek a suntanned appearance.

Bioaccumulation of chromium from tannery wastewater: an approach for chrome recovery and reuse.

The presence of chromium in the effluent is a major concern for the tanning industry. Currently, chemical precipitation methods are practiced for the removal of chromium from the effluent, but that leads to the formation of chrome-bearing solid wastes. The other membrane separation and ion exchange methods available are unfeasible due to their cost. In this study, the removal of chromium from tannery effluent has been carried out using abundantly available brown seaweed Sargassum wightii. Simulated chrome tanning solution was used for the standardization of experimental trials. Various factors influencing the uptake of chromium, viz., quantity of seaweed, concentrations of chromium, pH of the chrome-bearing wastewater, and duration of treatment, have been studied. Chemical modification of the seaweed through pretreatment with sulfuric acid, magnesium chloride, and calcium chloride showed improved uptake of chromium. Langmuir and Freundlich isotherms have been fitted for various quantities of seaweed. The dynamic method of treatment of protonated seaweed with simulated chrome tanning solution at a pH of 3.5-3.8 for a duration of 6 h gave the maximum uptake of about 83%. A similar uptake has been established for commercial chrome tanning wastewater containing the same concentration of chromium. The Sargassum species exhibited a maximum uptake of 35 mg of chromium per gram of seaweed. Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis, and flame photometry studies have been carried out to understand the mechanistic pathway for the removal of chromium. The potential reuse of chromium-containing seaweed for the preparation of basic chromium sulfate (tanning agent) has been demonstrated.

Regeneration of Exhausted Chrome Tanning Solutions from Leather Production as a Method Preventing Environmental Pollution with Chromium

Photochemical degradation of organic impurities in exhausted chrome tanning solutions is studied. A method for regeneration of these solutions is proposed, allowing reduction of chromium loss with wastewater.

Formation having a tanning gradient structure of collagen membrane by the pervaporation technique

A collagen was selected to study the membrane separation of the water/ethanol mixture by pervaporation. The membrane showed a preferential permeation of water, with a separation factor α = 50 (at 50 wt%). After being doped into a chromium sulfate aqueous solution, the membrane was tanned easily with a homogeneous chromium distribution, and the resultant showed excellent permselectivity (ca. α = 250) with only a slight depression of the water flux. The gradient-tanned membrane was prepared by the pervaporation technique. This membrane showed a close value (ca. α = 210, maximum value ca. α = 450) to that of the doped membrane, even by a short contact period with the tanning solution.

Chromium(III) salts recovery process from tannery wastewaters

Chromium(III) salts are the most widely used chemicals for tanning processes [1], but only 60% of the total chromium salt reacts with the hides. Therefore, about 40% of the chromium amount remains in the solid and liquid wastes (especially spent tanning solutions). The presence of chromium(III) and salts in the sludges of both the wastewater biological treatment plants or the chemical plants for recycling spent tanning liquors, represents an inconvenience for the safe reuse of these sludges and a cost forming factor for their disposal. Among the several proposed methods for chromium recovery [1–6], lime or sodium hydroxide precipitation and filter-pressing of the chromium hydroxide is the usual way to recover chromium salts from spent process solutions or from leaching solutions of residues of hides. However, usually the chromium salts quality must be improved for their reuse in tanning processes [7]. The integration of membranes in the treatment process for chromium recovery reduces the environmental impact, favours the reuse of both the protein residue and the biological plant sludges, reduces the consumption of chemicals and decreases the costs of waste disposal.