Trona Mineral Grade Sodium Carbonate As A Process Aid For The Hot Water Process
Authors: Dai Q. , Chung K.H. 
Published: March 2010

Trona is a mineral which contains over 90% of a mixture of sodium carbonate and bicarbonate. It is a raw material used in the production of sodium-containing substances. The batch extraction test results showed that the processibility curves obtained using trona as the process aid for the recovery of Athabasca bitumen from mined oil sands using the hot water process were similar to those for sodium carbonate. To achieve an optimum recovery similar to that by sodium hydroxide, it required a dosage of trona three to four times that of sodium hydroxide. However, since trona is much cheaper than sodium hydroxide and chemical grade alkalines, it makes a promising substitute for sodium hydroxide in the hot water process.

Introduction

Sodium hydroxide (NaOH) has been the process aid of choice, used in the hot water extraction process. A plant in Fort Saskatchewan has been the sole supplier of NaOH to Syncrude. At this plant, NaOH is a co-product of the chlor-alkali process(l) in chlorine production which is primarily used in the pulp and paper industry. In recent years, many paper mills in Western Canada have adopted non-chlorine based processes due to growing environmental concerns. The declining demand for chlorine has caused a significant reduction in NaOH production and, as a result, the price has escalated.

Attempts have been made in the past to seek NaOH replacements. Chemicals which have been tested as process aids in the hot water extraction process include sodium carbonate (Na2C03), sodium bicarbonate (NaHC03), sodium silicate (Na2Si03), and ammonium hydroxide (NH40H)(2,3). These inorganic bases, though not as strong as NaOH, have been shown to be quite effective. Optimum recoveries using these process aids were comparable to that with NaOH, although optimum dosages of these process aids were about two to three times greater than that of NaOH.

Economic studies have also been carried out by Syncrude(2) comparing the costs of using NaOH, Na2C03, and NaOH/Na2C03 mixture as process aids. Based on the price ratio of Na2C03 to NaOH as 3/4, it was concluded that the NaOH/Na2C03 mixture could be a viable option. On-site NaOH production via the causticizing process was also considered; this utilizes Na2C03 (soda ash) and calcium hydroxide (quicklime) as feedstocks. However, from an economic point of view, these proposals do not provide the incentive for commercial application since the price of chemical grade Na2C03 is not appreciably lower than that of NaOH. It becomes apparent that the realistic options of substituting or producing NaOH with chemical grade compounds are quite limited.

This paper summarizes briefly a recent development on NaOH production, which prompted us to investigate the possibility of substituting NaOH with a raw material sometimes used in NaOH production.

Trona

Trona is a natural mineral which consists mostly of Na2C03 and NaHC03. The typical composition of trona is shown in Table I. It is used as the raw material for commercial production of sodium-containing compounds, including NaOH(1). It has also been considered as a reagent for scrubbing sulphur dioxide in spray driers(4).