**1.1 Project information**

The Ilimaussaq complex is located within the Kommune Kujalleq, the municipality of southern Greenland (**Figure 1**). It is a peralkaline intrusion which contains rocks which are extremely enriched in sodium, iron and high fields strength elements including rare earth elements.

Within the complex is the Kvanefjeld deposit which consists of a measured resource (JORC 2012) of 143 million tonnes @ 1.2% REO, 303 ppm U3O8 and 0.24% zinc [1].

#### **Figure 1.**

*Map of Kommune Kualleq showing local population centres and project infrastructure.*

Greenland Minerals Limited (GML) proposes to develop a mine and integrated minerals processing facility for Kvanefjeld. In addition to producing significant quantities of REE products, the project will also produce, as by-products, small but commercially valuable quantities of uranium, zinc concentrate and fluorspar.

The rare earth elements, in the Kvanefjeld deposit, are contained predominantly in the mineral steenstrupine, which has the chemical formula provided below:

Na6*:*7HxCa REE ð Þ6ð Þ Th, U <sup>0</sup>*:*5ð Þ Mn1*:*6Fe1*:*8Zr0*:*3Ti0*:*1, Al0*:*<sup>2</sup> ð Þ P4*:*3Si1*:*<sup>7</sup> O24Þð Þ F, OH *:*nH2O*:*

It contains all 15 rare earth elements, radionuclides, phosphorous and soluble silica. Rare earths are also found to a lesser extent in the minerals townendite, monazite and vitusite [2].

Beneficiation of steenstrupine from the gangue minerals is possible via the froth flotation method. Froth flotation can be used to produce a steenstrupine mineral concentrate which typically grades 14–23% rare earth oxide [3, 4]. Gangue minerals such as felspars, feldspathoids, agerine and amphiboles are extensively rejected and report to the tailings stream. This paper will focus on the hydrometallurgical treatment of flotation concentrates as this is the typical process for rare earth recovery. The inventive aspect is in the definition of process variables which result in a leaching process which produces high extractions while exhibiting good solid liquid separation characteristics of leach residues.

### **1.2 Mineral leaching issues**

As steenstrupine is a very rare mineral there is little research and commercial precedent for it's treatment [5]. It contains a high degree of acid soluble silica and non*Concentrated Hydrochloric Acid Leaching of Greenland Steenstrupine to Obviate Silica Gel… DOI: http://dx.doi.org/10.5772/intechopen.107012*

refractory rare earth elements which makes it's leaching characteristics unusual. Historical leaching tests were performed on ore samples which contained steenstrupine [6]. This early work showed steenstrupine and some associated gangue minerals are susceptible to silica gelling. Steenstrupine and it's associated gangue silicate minerals contain acid soluble silica which dissolves into solution with acid leaching [7, 8].

Other researchers have found silica issues with another alkaline rare earth mineral Eudialyte which also contains significant soluble silica [8–10]. Silica soluble minerals which leach under acidic conditions will release silica into solution. If not carefully controlled, dissolved silica can precipitate rapidly forming a network structure in solution resulting in the solution gelling and exhibiting poor solid liquid separation [11–13].

Some leaching methods have been applied to steenstrupine which include both sulphuric and hydrochloric acids [1, 3, 7]. In 2012 GML developed a method which uses a two stage sulphuric acid leach to extract the values and control silica [7]. Since 2017, GML has been developing a different leaching method which utilises concentrated hydrochloric acid in a single stage leaching process [14]. Previous steenstrupine hydrochloric leach tests investigated low solids loading, relatively dilute acid solution and only batch operation [8]. This was effective in leaching rare earths from steenstrupine however a pyrometallurgical pre-treatment was required. In addition the leach density was moderately dilute.

This paper presents the results of investigating the leach performance at higher solids loading and concentrated acid concentrations without a pre-treatment step. The viability of the process is demonstrated by comparing batch leach results with those of continuous leach results.

## **2. Samples utilised**

#### **2.1 Low grade flotation concentrate**

The low grade flotation concentrate was generated from Kvanefjeld ore (Lujavrite) during continuous flotation pilot plant testwork. Mineralogical examination (QEM-SEM) identified steenstrupine, arfvedsonite, aegirine, analcime, K feldspar and plagioclase as the major components of the concentrate [3]. Elemental analysis of the concentrate used a combination of fusion inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectroscopy (ICP-MS). The chemical analysis was performed by the commercial SGS Laboratory in Perth, Australia who are certified and ISO accredited. The accuracy of the assays is considered very good with an accuracy of +/ 5% (**Table 1**).

Acid soluble silicon concentration in the concentrate was determined by diagnostic leaching of concentrate with 70 g/L Hydrochloric acid (HCl) for 2 hours at ambient


**Table 1.** *Low grade concentrate assays (% of mass).*


#### **Table 2.**

*High grade concentrate assays (% of mass).*

temperature at 1 and 3% w/w solids. The leach liquor was recovered and filtered through 0.45 microns before diluting 1:10 in deionised water and submitting for assay by Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES). The low solids density resulted in low silicon tenors in solution which prevented silica gelling issues. The acid soluble silicon concentration in the concentrate was determined to be 38 g of silicon per kilogramme of concentrate.

#### **2.2 High grade flotation concentrate**

Batch testwork on Kvanefjeld ore using an improved flotation process [3] generated a limited quantity of high-grade flotation concentrate which was available for leach testwork. The concentrate elemental composition was determined using a combination of sodium fusion and inductively coupled plasma. The elemental assays are shown in **Table 2**.

The acid soluble silicon concentration in the concentrate was determined to be 32 g of silicon per kilogramme of concentrate solids.
