Waste Tire Derived Materials to Treat Phosphate Processing Waste

Abstract

The process of obtaining phosphate from mining produces large amounts of waste. Finding an eco-friendly way of treating and/or valorising these by-products is of utmost importance for the phosphate processing industry, the settlements located near to the mine and processing plant and the environment in general. On the other hand, due to the fast development of the modern society, the transportation needs and therefore the number of tires produced to fulfill those requirements is increasing daily. When reaching their end-of-life those tires enter the waste stream creating a significant issue since they are very difficult to handle. The use of waste tire derived materials for the treatment of phosphate waste sludge could tackle both problems at once. This study focused on the use of waste tire crumb and the solid residue (char) of tire pyrolysis to adsorb trace elements (that are usually present in phosphate water effluents) from synthetic solutions. Cu and Ni where the minerals analysed in this case study. The behaviour of waste tire derived adsorbents in batch adsorption systems was studied varying the pH, contact time and cation to adsorbent quantity ratio. At optimum adsorption conditions, the potential adsorbent materials and their behaviour with the two heavy metal cations, differs. While char shows high affinity to adsorb Cu (>97% removal), crumb does not interact with this metal to a high extent giving a lower value (around 30%). On the other hand, for Ni, crumb performed slightly better than char although none of them reached 20% removal. When both cations were present simultaneously in the solution a negative impact on the Ni removal was noticeable for char, due to the leaching from the adsorbent. The adsorption process follows most likely an ion exchange mechanism. Therefore, this study shows the potential of waste tire derived materials for heavy metal cations removal from aqueous solutions.