Characterization of phosphate rock and phosphogypsum from Gabes phosphate fertilizer factories (SE Tunisia): high mining potential and implications for environmental protection

Abstract

Since the establishment of the coastal industrial complex in Gabes city (Gulf of Gabes, SE Tunisia), hundred million tons of untreated phosphogypsum have been discharged in the open sea causing serious environmental problems. To better understand the dynamic and behavior of phosphate/phosphogypsum contaminants from raw ores to marine environment, a chemical, organic, mineralogical, and morphological characterization of phosphate rock and phosphogypsum was conducted using several sophisticated techniques. The chemical analysis showed that phosphate and phosphogypsum contain high loads of trace elements and that the transfer factors of pollutants varied from 5.83% (U) to 140% (Hg). Estimated annual flows of phosphogypsum contaminants into the marine environment ranged between 0.05 (Re) and 87,249.60 (F) tons. The phosphate rock was found to be formed by carbonate fluorapatite, calcite, dolomite, natural gypsum, quartz, calcite-Mg, apatite, pyrite, fluorite, and sphalerite-Cd and phosphogypsum by synthetic gypsum and sphalerite-Cd. The phosphate was found to be richer in organic compounds compared to phosphogypsum. Based on this work, the Tunisian phosphogypsum has a high mining potential and encourages the development of an economically beneficial and environmentally friendly phosphogypsum-treating industry.

Overview on the removal of iron from phosphoric acid: A Comparative study

“…Wet process (WPA) is the most common method for phosphate fertilizers production, thermal process gives higher purity and is used in non fertilizer products, rotary kiln process is a promising method as it reduces the environmental footprint [4]. In the wet process, the mineral is treated with mineral acids that may be nitric, hydrochloric or sulfuric according to: Globally, most of phosphoric acid is manufactured by the wet process using sulfuric acid as leaching agent that has the advantage of forming an insoluble precipitate of calcium sulfate dihydrate (phosphogypsum, (10CaSO 4 .2H 2 O)) in addition to radionuclides and lanthanides that are coprecipitated [5][6][7][8]. Three fractions of phosphoric acid are produced depending on the process conditions namely: Dihydrate acid, WPA [ WPA contains many impurities that depend on the origin of phosphate ores and which render the phosphoric acid unsuitable for certain uses, such as, metal treatment, food ingredients and electronic applications, therefore, it must be purified before use.…”

Cadmium and iron removal from phosphoric acid using commercial resins for purification purpose

“…The thermal processing usually limits the presence of metal impurities, but the technique is highly expensive, nevertheless wet processing is the most frequently used at industrial scale. Its main drawback consists of the presence of relatively high concentrations of hazardous metals (such as uranium, cadmium, mercury, arsenic, and other heavy metals) or other organic (humic acid, for example) and inorganic substances (such as sulfate) (El Zrelli et al 2018). The requirements and regulations for phosphoric acid grade are of increasing complexity when target application concerns fertilizers < food < pharmacy < electronics.…”

Phosphogypsum Conversion into Calcium Fluoride and Sodium Sulfate

“…Although, PG is mainly formed by calcium sulfate (effectively dihydrate) beside numerous impurities such as: phosphates, fluorides, heavy metals, and radioelements. Hence, the presence of these impurities at higher than natural levels, can cause a severe environmental problem in long term [1][2][3].…”