          1 Application of full factorial design to optimize phosphogypsum beneficiation process (P 2 O 5 Reduction) by using sulfuric and nitric acid solutions Mohammad A. Aliedeh and Nabeel A. Jarrah Department of Chemical Engineering, Mutah University, P. O. Box 7, 61710, Karak, Jordan (maliedeh@mutah.edu.jo , aljarrahn@mutah.edu.jo ) Tel: +962 3 2372380, Fax: +962 3 2375540 Abstract Inventing new ways to recycle and reuse the accumulated by-products is the most pressing and daunting challenge that face future engineers. Millions of tons of phosphogypsum (PG) is stacked worldwide every year and is progressively considered as an asset more than an environmental burden. Jordan cement industry is largely expanded in the last ten years and is considered as an opening to reuse the huge amount of Jordanian PG that is stacked every year. The impurities that PG contains hinder its use as an additive to the cement industry which is pushing towards developing a low cost and effective process to clean PG. Many researches used a number of physical, chemical and thermal methods to reduce P 2 O 5 content in PG, but all of these studies are invariant, did not go deep in understanding the process of washing/leaching of P 2 O 5 and is not oriented towards developing a process. In this study, a multivariate 2 4 full factorial methodologies is designed to study the effect of particle size, acid concentration, loading and number of washing on the P 2 O 5 washing/leaching process using sulfuric and nitric acid solutions. The Factorial design analysis helped to get more insight on the relative magnitude of the main and the interaction effects. Sulfuric and nitric acid treatment results indicate clearly the importance of the number of washing on the reduction of P 2 O 5 content. This emphasized the importance of renewing the driving force (adding each time a clean solution). It is found that the optimum conditions for sulfuric acid treatment are to have a loading equal to 0.15 g PG/ g solution and three washings. The optimum conditions for nitric acid treatment are estimated to be loading of 0.4 g PG/ g solution and three washings. Keywords: Factorial design; Beneficiation; P 2 O 5 ; Phosphogypsum. 1. Introduction The world sailed in the new millennium with a huge burden of problems that need to be tackled. Financial crisis, global warming, climate change, wars and conflicts, food shortage, health issues, and environmental pollution are just a small portion of this big burden that the world faces. Environmental problems take the lead in this big list of challenges that humanity face nowadays and in the future. Designing an environmental friendly and sustainable products and processes is a major challenge for future engineers, in addition to the other important and pressing challenge which is alleviating the environmental effects of the accumulated by products by inventing new ways to recycle and reuse. Jordan has limited resources and this necessitates the adoption of stringent policies to conserve consumption, prevent pollution, and recycle waste materials for better use. Jordan was one of the world’s top producers of bromine, phosphate rock, and potash in 2009 [Mowafa Taib, 2011]. It also produced cement, clay, fertilizer, kaolin, limestone, pozzolanic material, refined petroleum products, silica sand, steel, and zeolitic tuff [Mowafa Taib, 2011]. Fertilizers industry, which is based on local potash and phosphates resources, is one the major pillars of the Jordanian economy. This important industry is mainly based on the production of phosphoric and sulfuric acid. Jordan annual production of phosphoric acid (using the wet process) can be estimated to be around 500 thousand metric ton [Mowafa Taib, 2011]. In addition to these big amount of phosphoric acid, a five times this quantity is stacked every year as phosphogypsum (by product of wet phosphoric acid production process) in Aqaba, Jordan. Many mineral production processes suffer from the generation of large amounts of mineral byproducts or wastes. Phosphogypsum is one of these mineral wastes that is accumulated in large a mounts all over the world. The world production of phosphogypsum is estimated to be 100-280 million tons a year that are traditionally stacked in piles. Several impact studies for the stacking of phosphogypsum show that this practice is an economical and an ecological burden that in need to be relieved [Reijnders, 2007]. Phosphogypsum (PG) is a by product of the phosphoric acid wet production process. PG is produced by reacting phosphate rock (raw material) with sulfuric acid according to the following chemical reaction. ( ) 10 4 2 2 4 2 3 4 4 6 10 20 6 10 2 Ca PO F H SO HO H PO CaSO HF + + → + + (1) The phosphogypsum produced appears as dihydrate (CaSO 4 .2H 2 O) or hemihydrate (CaSO 4 .1/2H 2 O) form,