Preparation of calcium sulfate whiskers using waste calcium chloride by reactive crystallization

Abstract

Calcium sulfate whiskers, owing to its good thermal stability, chemical resistance and good compatibility with rubber and plastics, has a strong potential in the application of polymer reinforcing composite materials. This work deals with the preparation of calcium chloride whiskers by reactive crystallization process with sulfuric acid and calcium chloride discharged from Solvay process. Firstly, the orthogonal experiments were carried out using both CaCl 2 and H 2 SO 4 in analytic grade as feedstock, and the reactive crystallization conditions were optimized, which included reaction temperature, reactant concentration, reaction time and stirring speed. Based on the optimized reactive crystallization conditions, the new process for the preparation of calcium chloride whiskers was studied using the reactive crystallization process with sulfuric acid and calcium chloride discharged from Solvay process, and the effects of impurity ions in the waste solutions on the growth of whiskers were evaluated. It was found that calcium sulfate whiskers with stable and structured fine crystals (its aspect ratio up to 190) can be prepared using waste CaCl 2 in Solvay process. The experimental results will provide the valuable information for the reasonable disposal of waste CaCl 2 solution from Solvay process.

Thermal Insulation from Construction Coating Mixed with Porous Calcium-containing Solid Waste

“…One thermal imaging apparatus was used to observe temperature distribution on each sample, meanwhile three thermocouples (K type) were used to detect surface temperatures of the painting. The surface 4 powders with low and high magnification, respectively. The photos reveal that the as-prepared powders have highly roughened surface.…”

“…Thus, the chemical-wet method shows a scalable feasibility for producing green architecture materials due to its simplicity, high efficiency, and easy operation. To examine its practical applicability for thermal insulation, the porous characteristics of as-prepared CaSO 4 powder is further analyzed by physical adsorption of nitrogen. The BET surface area and total pore volume of CaSO 4 powders are 102 m 2 /g and 0.23 cm 3 /g, respectively.…”

“…The as-prepared paintings were pasted on the substrates with a doctor blade and then dried at 80°C in an oven overnight. Nitrogen physisorption technique has been employed to analyze the surface characteristics of CaSO 4 powders. An automated adsorption apparatus (Micromeritics, ASAP 2020) was adopted to characterize the porous nature of CaSO 4 powders, using N 2 physisorption at -196°C.…”

“…Afterward, the solid waste was slowly added into 1 M H 2 SO 4 solution. The chemical process was carried out at ambient temperature for 1 h, allowing the formation of CaSO 4 or CaSO 4 · 2H 2 O with high chemical conversion. Finally, white powders were precipitated in the bottom of beaker and were dried at 105°C in an oven overnight.…”

“…Several approaches have been explored to synthesize calcium sulfate materials, using hydrothermal reaction [1], reactive crystallization Manuscript received December 15, 2016; revised February 1, 2017. Hsi-Chi Yang is with the Chung Hua University, China (e-mail: hcyangse@chu.edu.tw) [2]- [4], chemical extraction using organic media [5], and calcination-acidification [6]. Our strategy is to chemically transfer Ca(OH) 2 to CaSO 4 in the presence of diluted sulfuric acid.…”