An Advanced Organic Technology to Produce Chromium-Free Goat Leather: Insights and Methodology to Use Caesalpinia spinosa as a Tanning Agent

Chromium-based technique has been used over the decades and, up to now, is the most extended technology to produce leather around the world. However, the environmental problems related to its production, with special regard to the extremely high amounts of residual chromium in the soil and in the water, are reducing the use of leather, and it is becoming replaced with the use of synthetic materials. Consequently, the current leather production is becoming unsustainable due to the higher cost of treating the effluents derived from it. To eliminate the high consumption of this mineral, a Caesalpinia spinosa (Tara) tanning technique was developed and optimized on a semi-industrial scale. The reported results indicated that, being highly superior to the traditional methods, this was possible after an extensive Tara characterization, which reported, for example, (a) IRR reported strong vibration peaks in different positions, which suggested the presence of polyphenols as a principal component of the Tara powder. This assumption was confirmed by the tannic acid content, which reported values equal to 52.25 ± 1.74 mg/g of Tara powder. These results suggested that the Tara serves as a good tannin agent. This was proven by the mechanical characteristics of the leather produced by using Tara. For example, when 10% of Tara powder was applied to the formulation, the best results were obtained in all the mechanical characteristics of the leather. Thus, for the tensile strength, the average value was equal to 340.77 ± 4.78 N/mm2. Moreover, the sustainability of the process was demonstrated by the good wastewater quality, which showed a null concentration of chromium hexavalent and total chromium. As expected, the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) increased considerably, reaching values of 1461.00 mgO2/L and 3150.30 mgO2/L, respectively. Finally, the economic feasibility of the project was obtained through the cost/benefit and Internal Return Rate (IRR) analysis. The results reported a cost/benefit ratio equal to USD 1.03 and an IRR equal to 31%, thus the investment can be recovered after 5 years of execution of the project. This novel zero-chrome tanning process solves the long-standing environmental problems that have been linked to making leather and meets all the needs of today’s sustainable leather industry.