Internal coordination of vanadium industrial waste—Preparation of hydroxyapatite and fluorine wastewater purification

Abstract

In the vanadium industry, raffinate poses potential environmental risks due to the presence of corrosive fluoride and toxic heavy metals, and waste neutralizing slag (NS) was largely stockpiled given the low economic value, resulting in extensive land occupation and secondary pollution risks. Hydroxyapatite (HAP) was synthesized uniformly from the NS using the hydrothermal method, with no surfactants or additives used except for the three inexpensive reactants required. It was discovered that the pH of the raw material, the temperature, and the length of the hydrothermal reaction all had a significant effect on the adsorption characteristics of the produced HAP. When the conditions for synthesizing HAP were set with a pH of 11.5, a hydrothermal reaction temperature of 120 °C, and a reaction time of 1.5 h, the HAP had the optimum impact on raffinate treatment. The products' characterization by XRD, FTIR, SEM-EDS, and BET corroborated the successful synthesis of homogeneous HAP under the process conditions. The waste stream from the hydrothermal synthesis of HAP was recovered and crystallized to obtain a sodium sulfate by-product which was determined for purity. Adsorbed at room temperature for 1 h, the HAP synthesized by NS has a maximum percentage adsorption of 99.66 % and a saturation adsorption capacity of 43.64 mg/L for F ions in the raffinate. Additionally, the HAP removed over 95 % of the trace heavy metal ions Cr, As, and Cd from the raffinate. The saturated HAP was treated using a hydrothermal regeneration process, and the regenerated HAP retained a fluoride percentage adsorption still reaching 99.28 %. The thermodynamic and leaching experiments reveal that the desorption solution for the regeneration of HAP has the performance to increase the efficiency of vanadium recovery. This technique recycles waste NS to produce high-value HAP, which purification treatment of the raffinate with a high fluorine and contaminants content, solves the problem of treating two types waste of vanadium industry waste (NS and raffinate), and allows for the recycling of valuable element fluorine in vanadium industrial effluent.