Industrial symbiosis: Boron waste valorization through CO 2 utilization

Various wastes being generated globally and dumped on land by mineral processing activities pose great ecological and health problems. An example is the boron mineral beneficiation solid wastes. Even greater threat is anthropogenic carbon dioxide (CO 2 ) emissions among key causes of prevalent climate change. By this work, we propose a symbiotic solution to alleviate both environmental threats through recovering valuable boron products from boron wastes (BW), while also utilizing and sequestering CO 2 stably and permanently. This article presents the results on the effect of important operation parameters for the performance of such a process within the following ranges determined by preliminary tests: temperature: 20–60°C, solid-to-liquid ratio: 0.1–0.5 g/ml, reaction time: 15–120 min, stirring speed: 300–700 rpm and particle size: 150–600 µm. CO 2 gas (99.9%) flow rate was maintained continuously at 1.57 l/min under atmospheric pressure. The important findings are (1) per ton of BW production of commercially valuable either (a) 310 kg sodium penta-borate or (b) 350 kg sodium penta-borate mixed with Na 2 CO 3 , depending on the process configuration, (c) 725 kg relatively pure CaCO 3 , a potential source for precipitated calcium carbonate (PCC) and (d) 72 kg CO 2 utilization, (2) effective parameters for CO 2 utilization, in decreasing order are temperature, solid-to-liquid ratio and time, while stirring speed and particle size are ineffective within the range investigated and (3) the optimum operating conditions as: temperature: 60 °C, solid-to liquid ratio: 0.1 g/ml, time: 90 min, stirring speed: 500 rpm and particle size: <180 µm.